Heterocyclic-NMDA antagonists

ABSTRACT

The present invention is directed to a class of 3-phosphono-pyrrolidine derivatives as described by Formula I and their use as NMDA antagonists. ##STR1##

This is a continuation of application Ser. No. 07/986,222, filed Dec. 7,1992, now abandoned, which is a divisional of application Ser. No.07/675,156, filed Mar. 28, 1991, issued as U.S. Pat. No. 5,194,430 onMar. 16, 1993, which is a Continuation in part of application Ser. No.07/525,290, filed on May 17, 1990, now abandoned.

The present invention is directed to a class of 3-[functionalizedalkylphosphono]-piperidine and pyrrolidine compounds that are useful asNMDA antagonists. Another aspect of the invention is directed to the useof these compounds in the treatment of a number of disease states. Afurther aspect of this invention is directed to pharmaceuticalcompositions containing these compounds.

In accordance with the present invention a new class of NMDA antagonistshave been discovered which can be described by the following formula:##STR2## in which R₁ is represented by hydrogen, C₁₋₄ alkyl or CF₃ ; Mis represented by O, N--O--R₄ or ##STR3## in which R₄ is represented byhydrogen, C₁₋₄ alkyl or alkylphenyl;

A is represented by one of the following substituents: ##STR4## R₂ isrepresented by hydrogen, C₁ -C₄ alkyl, cycloalkyl, trialkylamino,alkylphenyl, phenyl, substituted phenyl, or trifluoromethyl; R₃ isrepresented by hydrogen, C₁ -C₄ alkyl, phenyl, alkylphenyl, orcyclohexylmethyl;

R₅ is represented by hydrogen, linear C₁ -C₄ alkyl, or alkylphenyl; R¹is represented by hydrogen, C₁ -C₄ alkyl, phenyl, alkylphenyl, orcyclohexylmethyl; or a pharmaceutically acceptable salt thereof. As usedin this application:

a) the terms "lower alkyl group and C₁ -C₄ alkyl" refer to a branched orstraight chained alkyl group containing from 1-4 carbon atoms, such asmethyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, etc;

b) the terms "lower alkoxy group and C₁ -C₄ alkoxy" refer to a straightor branched alkoxy group containing from 1-4 carbon atoms, such asmethoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, etc.;

c) the term "cycloalkyl" refers to a cyclohexyl or a cyclopentyl group;

d) the term "substituted phenyl ring" refers to a phenyl (C₆ H₅) whichis substituted with up to 3 substituents, each substituent isindependently selected from the group consisting of halogens, C₁ -C₄alkyl, C₁ -C₄ alkoxy, CF₃, OCF₃, OH, CN, COOR₆, and CONR₆ R₇ in which R₆and R₇ are represented by hydrogen or a C₁ -C₄ alkyl. These substituentsmay be the same or different and may be located at any of the ortho,meta, or para positions;

e) the term "phenyl(C₁ -C₃) substituent" refers to the followingstructure --(CH₂)_(m) --C₆ H₅, in which m is an integer from 1-3. Thisphenyl ring may be substituted in the manner described immediatelyabove;

f) the term "oxime" refers to compounds in which M is represented byN--O--R₄ ;

g) the term "hydrazone" refers to compound in which M is represented by,N--NH--R₄ ;

h) the term "pharmaceutically acceptable addition salt" refers to eithera pharmaceutically acceptable acid addition salt or a pharmaceuticallyacceptable basic addition salt;

i) the term "halogen" refers to a fluorine or chlorine atom;

j) the term "trialkylamino" refers to ##STR5## in which n is representedby an integer from 2-4 and Alk and Alk₁ are each independentlyrepresented by a C₁ -C₄ alkyl; and

k) the term "cyclohexylmethyl" refers to --CH₂ --C₆ H₁₂.

The expression "pharmaceutically acceptable acid addition salts" isintended to apply to any non-toxic organic or inorganic acid additionsalt of the base compounds represented by Formula I, or any of itsintermediates. Illustrative inorganic acids which form suitable saltsinclude hydrochloric, hydrobromic, sulphuric, and phosphoric acid andacid metal salts such as sodium monohydrogen orthophosphate, andpotassium hydrogen sulfate. Illustrative organic acids which formsuitable salts include the mono-, di-, and tricarboxylic acids.Illustrative of such acids are for example, acetic, glycolic, lactic,pyruvic, malonic, succinic, glutaric, fumaric, malic, tartaric, citric,ascorbic, maleic, hydroxymaleic, benzoic, hydroxy-benzoic, phenylacetic,cinnamic, salicyclic, 2-phenoxy-benzoic, p-toluenesulfonic acid, andsulfonic acids such as methane sulfonic acid and 2-hydroxyethanesulfonic acid. Such salts can exist in either a hydrated orsubstantially anhydrous form. In general, the acid addition salts ofthese compounds are soluble in water and various hydrophilic organicsolvents, and which in comparison to their free base forms, generallydemonstrate higher melting points.

The expression "pharmaceutically acceptable basic addition salts" isintended to apply to any non-toxic organic or inorganic basic additionsalts of the compounds represented by Formula I, or any of itsintermediates. Illustrative bases which form suitable salts includealkali metal or alkaline-earth metal hydroxides such as sodium,potassium, calcium, magnesium, or barium hydroxides; ammonia, andaliphatic, alicyclic, or aromatic organic amines such as methylamine,dimethylamine, trimethylamine, and picoline.

All of the compounds of Formula I contain at least two (2) asymetriccenters and thus will exist as diasteriosmers. Any reference to thesecompounds as well as their intermediates should be construed asencompassing a racemic mixture, a specific optical isomer or a pair ofenantiomers. The specific optical isomers can be synthesized as shownherein or can be recovered by techniques known in the art such aschromatography on chiral stationary phases, or resolution via chiralsalt formation and subsequent separation by selective crystallization.HPLC ion exchange chromatography may be utilized to separate only thediastereomers.

Examination of Formula I shows that some of the compounds contain acarbonyl function in the alkyl chain which is bonded to the 3-positionof the piperidinyl ring or the pyrrolidinyl ring. These compounds willexist in a state of tautomeric equilibrium in which the carbonylfunction will participate in a keto-enol equilibrium reaction. Thistautomerism may be depicted as follows: ##STR6##

As is readily apparent to those skilled in the art, the enol form ofthis molecule will also exist as geometrical isomers and thus can existin either the cis or trans orientation.

As is indicated by the R₃ substituent, the piperidine ring may befurther substituted at positions 4, 5, or 6. R₃ may optionally representup to 2 non-hydrogen substituents. Only one non-hydrogen substituentshould be located at any one position on the piperidine ring. If twonon-hydrogen substituents are present, they may be the same ordifferent. When R₃ is a non-hydrogen substituent, then this substituentmay be either syn or anti relative to the phosphono substituent.

As is indicated by the dotted line in the piperidinyl structure, adouble bond may exist at positions 3 or 4.

Illustrative examples of compounds encompassed by Formula I include:

3-(Phosphonoacetyl)piperidine-2-carboxylic acid;

3-(Phosphonoacetyl)piperidine-4-methyl-2-carboxylic acid;

3-[1-[(Phenylmethoxy)imino]-2-phosphonoethyl]piperidine-2-carboxylicacid;

3-(Phosphonoacetyl)piperidine-5-methyl-2-carboxylic acid;

3-[(1-Methoxyimino)-2-phosphonoethyl]piperidine-5-methyl-2-carboxylicacid;

3-(Phosphonoacetyl)piperidine-2-carboxylic acid, ethyl ester;

3-(Phosphonoacetyl)piperidine-5-(1-phenylmethyl)-2-carboxylic acid;

3--(Phosphonoacetyl)piperidine-4,5-dimethyl-2-carboxylic acid;

3-(PhosPhonoacetyl)piperidine-5-propyl-2-carboxylic acid;

3-[1-[(Phenylmethoxy)imino]-5-propyl-2-Phosphonoethyl]piperidine-2-carboxylicacid;

3-(Phosphonoacetyl)piperidine-5-methyl-2-carboxylic acid, ethyl ester;

3-(Phosphonoacetyl)piperidine-5-propyl-2-carboxylic acid, ethyl ester;

d,l-trans-3-(Phosphonoacetyl)piperidine-2-carboxylic acid;

d,l-cis-3-(Phosphonoacetyl)piperidine-2-carboxylic acid

3(S)-[(Diethoxyphosphinyl)acetyl]piperidine-2(R)-carboxylic acid, methylester;

3(S)-[(Diethoxyphosphinyl)acetyl]piperidine-4-methyl-2(R)-carboxylicacid, methyl ester;

3(R)-[(Diethoxyphosphinyl)acetyl]piperidine-4-methyl-2(S)-carboxylicacid, methyl ester;

3(S)-(Phosphonoacetyl]piperidine-4-methyl-2(R)-carboxylic acid;

3(R)-(Phosphonoacetyl]piperidine-4-methyl-2(S)-carboxylic acid;

3(S)-[(Diethoxyphosphinyl)acetyl]piperidine-5-methyl-2(R)-carboxylicacid, methyl ester;

3(S)-(Phosphonoacetyl]piperidine-5-methyl-2(R)-carboxylic acid;

d,l-cis-3-[(Diethoxyphosphinyl)acetyl]piperidine-2-carboxylic acid,methyl ester;

3(S)-(Phosphonoacetyl]piperidine-2(R)-carboxylic acid;

3(S)-(Phosphonoacetyl]piperidine-5-methyl-2(R)-carboxylic acid;

3(S)-(Phosphonoacetyl]piperidine-5-benzyl-2(R)-carboxylic acid;

3(S)-(Phosphonoacetyl]piperidine-3(R)-methyl-2(R)-carboxylic acid;

3(S)-(Phosphonoacetyl]piperidine-5-benzyl-3(R)-methyl-2 (R)-carboxylicacid;

3-(Phosphonoacetyl]-3-piperidene-2(R)-carboxylic acid;

3-(Phosphonoacetyl]-3-piperidene-5-methyl-2(R)-carboxylic acid;

3(S)-(Phosphonoacetyl]-4-piperidene-2(R)-carboxylic acid;

3(S)-(Phosphonoacetyl]-3(R)-methyl-4-piperidene-2(R)-carboxylic acid;

3(S)-(Phosphonoacetyl]-3(R)-methyl-5-methyl-4-piperidene-(R)-carboxylicacid;

3(S)-(Phosphonoacetyl]-3(R)-methyl-5-benzyl-4-piperidene-(R)-carboxylicacid;

d,l-cis-3-(Phosphonoacetyl]pyrrolidine-4-methyl-2-carboxylic acid;

d,l-trans-3-(Phosphonoacetyl]pyrrolidine-4-methyl-2-carboxylic acid

d,l-cis-3-(Phosphonoacetyl]pyrrolidine-2-carboxylic acid;

d,l-trans-3-(Phosphonoacetyl]pyrrolidine-2-carboxylic acid

d,l-cis-3-(Phosphonoacetyl]pyrrolidine-3-methyl-2-carboxylic acid;

d,l-trans-3-(Phosphonoacetyl]pyrrolidine-3-methyl-2-carboxylic acid.

It is preferred for A to be a saturated piperidine ring and for M to beO. R₃ and R₅ are preferably hydrogen. The preferred stereo-chemistry is2R,3S.

The saturated piperidine compounds of Formula I in which M isrepresented by O and R₅ is represented by hydrogen, can be preparedutilizing techniques known in the art. One method for preparing thesecompounds is illustrated below in Reaction Scheme A. In Scheme A, allsubstituents are as previously defined unless otherwise indicated.##STR7##

Scheme A provides a general synthetic procedure for preparing thesaturated piperidine compounds of Formula I in which M is represented byO and R₅ is represented by hydrogen.

In step a, the appropriate pyridine-2,3-dicarboxylic acid derivative ofstructure (1) is reduced to give the correspondingpiperidine-2,3-dicarboxylic acid derivative of structure (2) usingtechniques and procedures well known in the art.

For example, the appropriate pyridine-2,3-dicarboxylic acid derivativeof structure (1) is contacted with an appropriate reducing agent, suchas nickel/aluminum, palladium, or platinum in the presence of hydrogen,nickel/aluminum being preferred. The reactants are typically contactedin aqueous base such as sodium hydroxide. The reactants are typicallystirred together for a period of time ranging from 6 hours to 5 days andat a temperature range of from 20°-38° C. Thepiperidine-2,3-dicarboxylic acid derivative of structure (2) isrecovered from the reaction zone by removing the catalyst by filtration.It may be used in solution without isolation or recovered by extractionand purification by chromatography.

In step b, the appropriate piperidine-2,3-dicarboxylic acid derivativeof structure (2) is protected to give the correspondingN-protected-piperidine-2,3-dicarboxylic acid derivative of structure(3). A variety of protecting groups may be utilized such as, forexample, benzyloxycarbonyl (CBZ). Other suitable protecting groupsinclude substituted carbamates such as t-butyloxycarbonyl andphenylfluorenyl (PhF).

These protecting groups may be placed on the nitrogen atom by techniquesknown in the art. If the protecting group is CBZ, for example, theappropriate piperidine-2,3-dicarboxylic acid derivative of structure (2)is contacted with a molar excess of benzyl chloroformate or[2-(tert-butoxycarbonyloxyimino)-2-phenylacetonitrile] or9-phenylfluorenyl bromide. The reactants are typically contacted in asuitable organic solvent such as aqueous dioxane. The reactants aretypically stirred together at room temperature for a period of timeranging from 2-24 hours. The N-protected-piperidine-2,3-dicarboxylicacid derivative of structure (3) is recovered from the reaction zone byextractive methods as is known in the art. It may be purified byrecrystallization.

Alternatively, if the protecting group is N-(9-phenylfluorenyl), forexample, the appropriate piperidine-2,3-dicarboxylic acid derivative ofstructure (2) is contacted with a molar excess of 9-phenylfluorenylbromide, a molar excess of a suitable base such as diisopropylethylamineand a molar deficiency of lead nitrate. The reactants are typicallycontacted in a suitable organic solvent such as acetonitrile. Thereactants are typically stirred together at room temperature for aperiod of time ranging from 2-24 hours. TheN-(9-phenylfluorenyl)piperidine-2,3-dicarboxylic acid derivative ofstructure (3) is recovered from the reaction zone by extractive methodsas is known in the art. It may be purified by silica gel chromatography.

In step c, the 2,3-dicarboxylic acid functionality of the appropriateN-protected-piperidine-2,3-dicarboxylic acid derivative of structure (3)is dehydrated to give the corresponding N-protected-piperidino anhydridederivative of structure (4).

For example, the N-protected-piperidine-2,3-dicarboxylic acid derivativeof structure (3) is contacted with a molar excess of acetic anhydride.The reactants are typically stirred together for a period of timeranging from 2-3 days at temperature range of from 20°-100° C. under aninert atmosphere such as nitrogen. The N-protected-piperidino anhydridederivative of structure (4) is recovered from the reaction zone byevaporation of the solvent.

In step d, the appropriate N-protected-piperidino anhydride derivativeof structure (4) is coupled with the appropriate phosphonate ester ofstructure (5) to give the correspondingN-protected-3-[(dialkoxyphosphinyl)acetyl]piperidine-2-carboxylic acidof structure (6). The appropriate phosphonate ester of structure (5) isone in which R₁ is represented by a C₁ -C₄ alkyl or a trifluoromethylgroup. These alkyl functionalities serve to act as protecting groupsduring the coupling reactions. One of these R₁ functions will be cleavedduring the deprotection reaction of optional step h₂ which is describedbelow and the second may also be hydrolysed if desired as described inoptional step i which is described below. Alternatively, both protectinggroups may be hydrolysed in one step as described in optional step g₁which is described below. As is obvious to those skilled in the art, theparticular protecting group utilized should correspond to that desiredin the final product if R₁ is not to be represented by hydrogen in thefinal product.

For example, the appropriate phosphonate ester of structure (5) is firstcontacted with a molar equivalent of an appropriate strongly basicreagent such as n-butyllithium. The reactants are typically contacted ina suitable organic solvent such as tetrahydrofuran under an inertatmosphere such as nitrogen. The reactants are typically stirredtogether for a period of time ranging from 10-20 minutes and at atemperature of -78° C. At that point the reaction medium is warmed toabout -10° C. and a molar equivalent of the appropriateN-protected-piperidino anhydride derivative of structure (4) is thenadded. The reactants are typically stirred together for a period of timeranging from 1-3 hours at a temperature range of from -78° C. to -20° C.The N-protected-3-[(dialkoxyphosphinyl)acetyl]piperidine-2-carboxylicacid of structure (6) is recovered from the reaction zone by extractivemethods as is known in the art. It may be purified by chromatography.

In step e, the 2-carboxylic acid functionality of the appropriateN-protected-3-[(dialkoxyphosphinyl)acetyl]piperidine-2-carboxylic acidof structure (6) is protected as its benzyl or C₁ -C₄ alkyl ester togive the correspondingN-protected-3-[(dialkoxyphosphinyl)acetyl]piperidine-2-carboxylic acid,benzyl or C₁ -C₄ alkyl ester of structure (7). These protecting groupscan be placed on the molecule using techniques known in the art.

For example, the appropriateN-protected-3-[(dialkoxyphosphinyl)acetyl]piperidine-2-carboxylic acidof structure (6) is contacted with a molar excess of an alkyl bromide ofthe formula R₂ "Br, wherein R₂ " is represented by benzyl or C₁ -C₄alkyl, and a molar excess of an appropriate non-nucleophilic base suchas dicyclohexyl amine. The reactants are typically contacted in asuitable aprotic solvent such as dimethylformamide in an inertatmosphere such as nitrogen. The reactants are typically stirredtogether for a period of time ranging from 1-4 hours and at atemperature range of from 20° to 65° C. TheN-protected-3-(dialkoxyphosphinyl)acetyl]piperidine-2-carboxylic acid,benzyl or C₁ -C₄ alkyl ester of structure (7) is recovered from thereaction zone by extractive methods as is known in the art. It may bepurified by chromatography.

In step f, the N-protecting group of the appropriateN-protected-3-[(dialkoxyphosphinyl)acetyl]piperidine-2-carboxylic acid,benzyl or C₁ -C₄ alkyl ester of structure (7) is removed to give thecorresponding 3-[(dialkoxyphosphinyl)acetyl]piperidine-2-carboxylicacid, benzyl or C₁ -C₄ alkyl ester of structure (8).

For example, the appropriateN-protected-3-[(dialkoxyphosphinyl)acetyl]piperidine-2-carboxylic acid,benzyl or C₁ -C₄ alkyl ester of structure (7) is contacted with a molarexcess of an appropriate such as aqueous hydrochloric acid,trifluoroacetic acid or a mixture of hydrochloric acid in dioxane. Thereactants are typically stirred together at room temperature for aperiod of time ranging from 1-5 hours. The3-[(dialkoxyphosphinyl)acetyl]piperidine-2-carboxylic acid, benzyl or C₁-C₄ alkyl ester of structure (8) is recovered from the reaction zone byneutralization with propylene oxide followed by filtration or bychromatography.

In optional step g₁, the 2-carboxylic acid ester and both of thephosphonate ester functionalities of the appropriate3-[(dialkoxyphosphinyl)acetyl]piperidine-2-carboxylic acid, benzyl or C₁-C₄ alkyl ester of structure (8) are removed to give the3-(phosphonoacetyl)piperidine-2-carboxylic acid of structure (9).

For example, the appropriate3-[(dialkoxyphosphinyl)acetyl]piperidine-2-carboxylic acid, benzyl or C₁-C₄ alkyl ester of structure (8) is typically contacted with a 3 to 6molar solution of hydrochloric acid. The reactants are typically stirredtogether at a temperature range of from room temperature to reflux for aperiod of time ranging from 1 to 30 hours. The3-(phosphonoacetyl)piperidine-2-carboxylic acid of structure (9) isrecovered from the reaction medium by techniques known in the art suchas precipitation as its free base with propylene oxide. It may then bepurifed by recrystallization from a solvent system such as, for example,ethanol/isopropanol.

In optional step g₂, the 2-carboxylic acid ester functionality of theappropriate 3-[(dialkoxyphosphinyl)acetyl]piperidine-2-carboxylic acid,benzyl or C₁ -C₄ alkyl ester of structure (8) is removed to give the3-[(dialkoxyphosphinyl)acetyl]piperidine-2-carboxylic acid of structure(10).

For example, appropriate3-[(dialkoxyphosphinyl)acetyl]piperidine-2-carboxylic acid, benzyl or C₁-C₄ alkyl ester of structure (8) is typically contacted with a 1 to 3molar solution of hydrochloric acid. The reactants are typically stirredtogether at a temperature range of from room temperature to reflux for aperiod of time ranging from 1 to 18 hours. The3-[(dialkoxyphosphinyl)acetyl]piperidine-2-carboxylic acid of structure(10) is recovered from the reaction medium by techniques known in theart such as such as precipitation as its free base with propylene oxide.It may then be purifed by recrystallization from a solvent system suchas, for example, ethanol/isopropanol.

In optional step h₁, the 2-carboxylic acid functionality of theappropriate 3-(phosphonoacetyl)piperidine-2-carboxylic acid of structure(9) is reesterified to give the3-(phosphonoacetyl)piperidine-2-carboxylic acid, ester of structure(11).

For example, the appropriate 3-(phosphonoacetyl)piperidine-2-carboxylicacid of structure (9) is contacted with an acidic solution of thedesired alcohol. The reactants are typically refluxed for a period oftime ranging from 2-24 hours. The3-(phosphonoacetyl)piperidine-2-carboxylic acid, ester of structure (11)is recovered from the reaction zone by extractive methods as is known inthe art. It may be purified by chromatography.

Alternatively, the appropriate3-(phosphonoacetyl)piperidine-2-carboxylic acid of structure (9) can becontacted with compound of the formula R₂ Br in which R₂ represents thedesired R₂ substituent. The reactants are typically contacted indimethyl formamide in the presence of a base such as dicyclohexylamine.The 3-(phosphonoacetyl)piperidine-2-carboxylic acid, ester of structure(11) is recovered from the reaction zone by extractive methods as isknown in the art. It may be purifed by chromatography. Other suitableesterification methods may also be utilized.

One of the protecting groups of the phosphonate ester, represented by R₁', is removed and depending upon the manner in which the deprotectionreaction is carried out, the other protecting group represented by R₁ 'may also be removed.

In optional step h₂, one of the phosphonate ester functionalites of theappropriate 3-[(dialkoxyphosphinyl)acetyl]piperidine-2-carboxylic acidof structure (10) is hydrolyzed to give the corresponding3-[(monoalkoxyphosphinyl)acetyl]piperidine-2-carboxylic acid ofstructure (12).

For example, appropriate3-[(dialkoxyphosphinyl)acetyl]piperidine-2-carboxylic acid of structure(10) is typically contacted with a 2 to 5 molar solution of hydrochloricacid. The reactants are typically stirred together at a temperaturerange of from room temperature to reflux for a period of time rangingfrom 1 to 18 hours. The3-[(monoalkoxyphosphinyl)acetyl]piperidine-2-carboxylic acid ofstructure (12) is recovered from the reaction medium by techniques knownin the art such as precipitation as its free base with propylene oxide.It may then be purifed by recrystallization from a solvent system suchas, for example, ethanol/isopropanol.

In optional step i, the remaining phosphonate ester functionality of theappropriate 3-[(monoalkoxyphosphinyl)acetyl]piperidine-2-carboxylic acidof structure (12) is hydrolyzed to give the3-(phosphonoacetyl)piperidine-2-carboxylic acid of structure (9).

For example, appropriate3-[(monoalkoxyphosphinyl)acetyl]piperidine-2-carboxylic acid ofstructure (12) is typically contacted with a 3 to 6 molar solution ofhydrochloric acid. The reactants are typically stirred together at atemperature range of from 60° C. to reflux for a period of time rangingfrom 1 to 30 hours. The 3-(phosphonoacetyl)piperidine-2-carboxylic acidof structure (9) is recovered from the reaction medium by techniquesknown in the art such as such as precipitation as its free base withpropylene oxide . It may then be purifed by recrystallization from asolvent system such as, for example, ethanol/isopropanol.

Alternatively, all 4 protecting groups (ie. Pg, R₂ ", and both R₁ 'functionalities) can be removed by combining step f and-step g₁ andsubjecting theN-protected-3-[(dialkoxyphosphinyl)acetyl]piperidine-2-carboxylic acid,benzyl or C₁ -C₄ alkyl ester of structure (7) to a vigorous acidichydrolysis. This can be accomplished by contacting the appropriateN-protected-3-[(dialkoxyphosphinyl)acetyl]piperidine-2-carboxylic acid,benzyl or C₁ -C₄ alkyl ester of structure (7) with a 6 molar solution ofa mineral acid such as HCL for a period of time ranging from 18 to 24hours at a temperature range of from room temperature to reflux. The3-(phosphonoacetyl)piperidine-2-carboxylic acid of structure (9) can berecovered from the reaction zone by techniques known in the art such assuch as precipitation as its free base with propylene oxide. It may thenbe purified by recrystallization from a solvent system such as, forexample, ethanol/isopropanol.

Also, where the 2-carboxylic acid ester functionality of the appropriate3-[(dialkoxyphosphinyl)acetyl]piperidine-2-carboxylic acid, benzyl or C₁-C₄ alkyl ester of structure (8) is benzyl or t-butyl, both of thephosphonate ester functionalities may be removed to give the3-(phosphonoacetyl)piperidine-2-carboxylic acid, benzyl or t-butyl esterof structure (11).

For example, the appropriate3-[(dialkoxyphosphinyl)acetyl]piperidine-2-carboxylic acid, benzyl ort-butyl ester of structure (8) is contacted with a molar excess oftrimethylsilylbromide or trimethylsilyliodide. The reactants aretypically contacted in a suitable organic solvent such as methylenechloride or acetonitrile. The reactants are typically stirred togetherat room temperature for a period of time ranging from 4-24 hours. The3-(phosphonoacetyl)piperidine-2-carboxylic acid, benzyl or t-butyl esterof structure (11) is recovered from the reaction zone by techniquesknown in the art such as such as precipitation as its free base withpropylene oxide. It may then be purified by recrystallization from asolvent system such as, for example, ethanol/isopropanol.

The proper starting material for the reduction of step a is apyridine-2,3-dicarboxylic acid derivative of structure (1), in which R₃is represented by the same substituent as is desired in the finalproduct. Starting materials for use in Scheme A are readily availiableto one of ordinary skill in the art. For example, certainpyridine-2,3-dicarboxylic acid derivatives are described in J. Med.Chem. 10, 1065 1974 and certain phosphonate esters of structure (5) aredescribed in Tetrahedron Letters 22 2829-31 1976.

The following examples present typical syntheses as described in SchemeA. These examples are understood to be illustrative only and are notintended to limit the scope of the present invention in any way. As usedherein, the following terms have the indicated meanings: "g" refers tograms; "mmol" refers to millimoles; "mL" refers to milliliters; "bp"refers to boiling point; "top" refers to melting point; "°C." refers todegrees Celsius; "mm Hg" refers to millimeters of mercury; "μL" refersto microliters; "μg" refers to micrograms; and "μM" refers tomicromolar.

Example 1

3-(Phosphonoacetyl)piperidine-2-carboxylic acid ##STR8## Step a:Piperidine-2,3-dicarboxylic acid

Dissolve pyridine-2,3-dicarboxylic acid (20 g, 120 mmol) in 0.5N aqueoussodium hydroxide (900 mL). Add nickel/aluminum powder (45 g) in portionsover 3 hours. Stir for 4 days, filter off the catalyst to yield thetitle compound in clear solution. The resulting free amine is notisolated.

Step b: N-Carbobenzoxypiperidine-2,3-dicarboxylic acid

Add benzyl chloroformate (20 mL, 167 mmol) to the above solution ofpiperidine-2,3-dicarboxylic acid (120 mmol) along with dioxane (200 mL).Stir overnight and acidify to a pH of 1 with 6N hydrochloric acid.Extract with methylene chloride (400 mL) followed by ethyl acetate (200mL). Combine the organic phases and dry (MgSO₄). Evaporate the solventin vacuo to give a clear oil (35.9 g, 98%). Recrystallize (chloroform)to give the title compound as a white solid as predominantly the transD,L compounds (10.9 g). Evaporate the residue to give the title compoundas a white semi-solid as approprimately a 2:1 cis/trans mixture ofdiastereomers.

¹ H NMR (300 MHz, d₆ DMSO) ppm 12.9 (bs), 7.35 (m), 5.2 (m), 4.5 (s),3.9 (d), 2.6 (s), 3.4 (m), 3.15 (s), 3.1 (m), 2.8 (m), 2.6 (m), 2.1 (m),1.9 (m), 1.6 (m), 1.45 (m).

Step c: N-Carbobenzoxypiperidine-2,3-dicarboxylic acid anhydride

Dissolve the 2:1 cis/trans mixture ofN-carbobenzoxypiperidine-2,3-dicarboxylic acid diastereomers (20 g) inacetic anhydride (500 mL) and stir overnight under a dry nitrogenatmosphere. Vacuum distill off the acetic anhydride to leave the titlecompound as a red glass (11.1 g, 59%).

¹ H NMR (90 MHz, CDCl₃) ppm 7.3 (s), 5.4 (m), 5.2 (s), 4.0 (m), 3.1 (m),2.9 (m), 2.2 (m). 1.7 (m).

Step d:N-Carbobenzoxy-3[(diethoxyphosphinyl)acetyl]piperidine-2-carboxylic acid

Dissolve methyl diethyl phosphonate (5.5 g, 36.4 mmol) in anhydroustetrahydrofuran (150 mL) and place under a dry nitrogen atmosphere. Coolto -78° C. and add n-butyllithium (14.0 mL of a 2.6M solution, 36.4mmol). Stir for 10 minutes and quickly add a precooled -60° C. solutionof N-carbobenzoxypiperidine-2,3-dicarboxylic acid anhydride (11 g, 3.8mmol) in anhydrous tetrahydrofuran (150 mL). Stir for 2 hours at -78° C.and allow to warm to -20° C. over 11/2 hours. Pour the reaction mixtureinto 1.0N hydrochloric acid (11/2 L) and extract with methylene chloride(2×500 mL). Combine the organic phases, dry (MgSO₄) and evaporate thesolvent in vacuo to give the title compound.

Step e:N-Carbobenzoxy-3[(diethoxyphosphinyl)acetyl]piperidine-2-carboxylic acidbenzyl ester

DissolveN-carbobenzoxy-3[(diethoxyphosphinyl)acetyl]piperidine-2-carboxylic acid(36.4 mmol) in dimethylformamide (200 mL) and place under a nitrogenatmosphere. Add benzyl bromide (10.5 mL), 81 mmol) and dicyclohexylamine (16.2 mL, 89 mmol) and heat to 65° C. Allow to cool slowly to roomtemperature and filter. Pour the filtrate into water (11/2 L) andextract with ethyl acetate (2×500 mL). Combine the organic phases anddry (MgSO₄). Evaporate the solvent in vacuo to give a brown oil. Purifyby flash chromatography (ethyl acetate) to give the title compound as ayellow oil (3.6 g, 19%).

Step f: 3-(Phosphonoacetyl)piperidine-2-carboxylic acid

Mix N-carbobenzoxy-3[(diethoxyphosphinyl)acetyl]piperidine-2-carboxylicacid benzyl ester (3.6 g) and 6N hydrochloric acid (400 mL) and refluxfor 24 hours. Condense with a stream of nitrogen and dissolve theresidue in a mixture of absolute ethanol (75 mL) and isopropanol (75mL). Filter and add propylene oxide until a white precipitate develops.Filter the precipitate, wash with isopropanol and dry to give the titlecompound as a white powder (1.55 g, 91%).

MS (FAB/glycerol) 252(M+H); ¹ H NMR (3000 mHz, D₂ O) ppm 4.6 (m), 4.4(m), 4.3 (m), 4.15 (d), 4.05 (d), 3.85 (m), 3.75 (d), 3.7 (d), 3.65 (q),3.45 (m), 3.4 (m), 3.1 (m), 3.05 (d), 3.0 (d), 2.85 (d), 2.45 (m) 2.4(m), 2.2 (m), 2.1 (m), 2.05 (m), 1.95 (m), 1.85 (m), 1.8 (m), 1.75 (m),1.6 (m), 1.55 (m), 1.45 (m), 1.2 (d), 1.115 (t).

¹³ C NMR ppm 212.0, 211.9, 211.7, 174.1, 173.8, 60.3, 60.2, 59.3, 59.2,50.7, 50.0, 46.7, 45.8, 27.2, 26.4, 25.8, 22.6, 21.0, 19.5.

³¹ p NMR (decoupled) ppm 12.56 and 12.42. Anal. Calcd for C₈ H₁₄ NO₆P.1.5H₂ O: C, 34.54, H, 6.07; N, 5.11; Found: C, 34.76; H, 5.58; N,4.69.

The saturated piperidine compounds of Formula I in which M isrepresented by O and R₅ is represented by hydrogen can be separated intotheir diastereomeric pairs as shown in Scheme B. In Scheme B, allsubstituents unless otherwise indicated are as previously defined##STR9##

Scheme B provides a general synthetic procedure for preparing theseparate diastereomeric pairs of the saturated piperidine compounds ofFormula I in which M is represented by O and R₅ is represented byhydrogen. For example, the appropriate 3-[(functionalizedphosphinyl)acetyl]piperidine-2-carboxylic acid derivative of structure(13) is separated to give the corresponding d,l-trans-3-[(functionalizedphosphinyl)acetyl]piperidine-2-carboxylic acid derivative of structure(14a) and the corresponding d,l-cis-3-[(functionalizedphosphinyl)acetyl]piperidine-2-carboxylic acid derivative of structure(14b) by High Performance Liquid Chromatography (HPLC).

The proper starting material for the separation is a compound of FormulaI as depicated by structure (13), in which R₃, R₁, and R₂ arerepresented by the same substituents as are desired in the finalproduct.

The following examples present typical syntheses as described in SchemeB. These examples are understood to be illustrative only and are notintended to limit the scope of the present invention in any way.

Example 2

d,l-trans-3-(Phosphonoacetyl)piperidine-2-carboxylic acid andd,l-cis-3-(Phosphonoacetyl)piperidine-2-carboxylic acid ##STR10##

The chromatographic conditions for the separation ofd,l-trans-3-(phosphonoacetyl)piperidine-2-carboxylic acid andd,l-cis-3-(phosphonoacetyl)piperidine-2-carboxylic acid are given below:

Column: 10-um Whatman Partisil SAX (250×4.6 nm).

Mobile Phase: 10/90 (v/v) acetonitrile/water, made 0.025M inhydrochloric acid.

Flow Rate: 1 mL/min.

Detection: λ=210 nm

Injection: 2 mL of a 1 mg/mL aqueous solution

Collect the fractions corresponding to the diastereomers using switchingvalves down stream from the detector. These valves are controled by theHPLC system. Freeze dry the collected fractions to give the separatedtitle compounds.

d,l-trans-3-(Phosphonoacetyl)piperidine-2-carboxylic acid

¹ H-NMR (300 MHz, NaOD) ppm 3.16 (d, J=9.9), 3.10 (m), 3.04 (m), 2.98(m), 2.78 (m), 2.55 (t, J=12.1), 2.14 (dm, J=12.4), 1.68 (dm, J=12.3),1.56 (qm, J=12.4), 1.46 (m).

d,l-cis-3-(Phosphonoacetyl)piperidine-2-carboxylic acid

¹ H-NMR (300 MHz, D₂ O) ppm 3.78 (d, 1), 3.69 (m, 1), 3.38 (m, 1),3.22-2.93 (m, 3), 2.32 (m, 1), 1.95 (m, 1), 1.79 (m, 1), 1.52 (m, 1).

Those saturated piperidine compounds of Formula I in which M isrepresented by either an oxime or a hydrazone derivative and R₅ isrepresented by hydrogen can also be prepared using techniques known inthe art. One method for preparing these compounds is disclosed below inScheme C. In Scheme C, all substituents unless otherwise indicated areas previously defined. ##STR11##

Scheme C provides a general synthetic procedure for preparing thesaturated piperidine compounds of Formula I in which M is represented byan oxime or a hydrazone derivative and R₅ is represented by hydrogen.

In step a, a condensation reaction is carried out between theappropriate 3-[(functionalized phosphinyl)acetyl]piperidine-2-carboxylicacid derivative of structure (13) in which R₁, R₂, and R₃ arerepresented by the same substituents as is desired in the final product,and in which M is O as is depicted, and one of the oximes or hydrazonesof structure (15) corresponding to the M substituent that is desired inthe final product. The condensation reaction can be carried out usingtechniques known in the art. Typically approximately equivalent amountsof the compound of Formula I and the oxime or hydrazone of structure(15) are contacted in a buffered solution. Sodium acetate is onesuitable buffer. The reaction is typically carried out at a temperaturerange of from 25° to 80° C. for a period of time ranging from 1 to 24 h.The desired 3-[1-imino-2-phosponoethyl]piperidine-2-carboxylic acidderivative of structure (16) can then be recovered from the reaction andpurified by either gel filtration or ion exchange chromatography.

In optional step b, the diastereomeric pairs of the appropriate3-[1-imino-2-phosponoethyl]piperidine-2-carboxylic acid derivative ofstructure (16) are separated to give thed,l-trans-3-[1-imino-2-phosponoethyl]piperidine-2-carboxylic acidderivative of structure (17a) andd,l-cis-3-[1-imino-2-phosponoethyl]piperidine-2-carboxylic acidderivative of structure (17b) as described previously in Scheme B.

Starting materials for use in Scheme C are readily availiable to one ofordinary skill in the art.

A synthesis for the enatiomerically pure 2(R)-, 3(S)-saturatedpiperidine compounds of Formula I wherein R₅ is represented by hydrogenis described in Scheme D. In Scheme D, all substituents unless otherwiseindicated is as previously defined. ##STR12##

Scheme D provides an alternative synthetic scheme for preparing theenatiomerically pure 2(R)-,3(S)-saturated piperidine compounds ofFormula I wherein R₅ is represented by hydrogen.

In step a, the appropriate pyridine-2,3-dicarboxylic acid derivative ofstructure (1) is protected to give the correspondingpyridine-2,3-dicarboxylic acid, diester derivative of structure (18).

For example, the appropriate pyridine-2,3-dicarboxylic acid derivativeof structure (1) is contacted with a molar excess of the appropriatealcoholic hydrochloric acid. The reactants are typically stirredtogether for a period of time ranging from 2-24 hours and at atemperature range of from room temperature to reflux. Thepyridine-2,3-dicarboxylic acid, diester derivative of structure (18) isrecovered from the reaction zone by evaporation of the solvent.

In step b, the appropriate pyridine-2,3-dicarboxylic acid, diesterderivative of structure (18) is reduced to give the correspondingd,l-cis-piperidine-2,3-dicarboxylic acid, diester derivative ofstructure (19).

For example, the appropriate pyridine-2,3-dicarboxylic acid, diesterderivative of structure (18) is contacted with an appropriate reducingagent such as palladium hydroxide in the presence of hydrogen. Thereactants are typically contacted in a suitable organic solvent such asmethanol. The reactants are typically shaken together at a pressure of45-50 psi for a period of time ranging from 6 hours to 5 days and at atemperature range of from 20°-38° C. Thed,l-cis-piperidine-2,3-dicarboxylic acid, diester derivative ofstructure (19) is recovered from the reaction zone by evaporation of thesolvent.

In step c, the appropriate d,l-cis-piperidine-2,3-dicarboxylic acid,diester derivative of structure (19) is separated via an enzymatichydrolysis into the corresponding enantiomerically purepiperidine-2(R),3(S)-dicarboxylic acid, diester derivative of structure(20a) and piperidine-2(S)-carboxylic acid-3(R)-carboxylic acid,monoester derivative of structure (20b).

For example, the appropriate d,l-cis-piperidine-2,3-dicarboxylic acid,diester derivative of structure (19) is contacted with a molar excess ofa suitable esterase such as porcine liver esterase. The reactants aretypically contacted in a suitable buffered solvent system such as pH 7.4phosphate buffer. The reactants are typically stirred together at roomtemperature for a period of time ranging from 10-48 hours. Theenantiomerically pure piperidine-2(R),3(S)-dicarboxylic acid, diesterderivative of structure (20a) is recovered from the reaction mixture byextractive methods as is known in the art and the enantiomerically purepiperidine-2(S)-carboxylic acid-3(R)-carboxylic acid, monoesterderivative of structure (20b) can be recovered from the reaction zoneion-exchange chromatography.

In step d, the appropriate piperidine-2(R),3(S)-dicarboxylic acid,diester derivative of structure (20a) is protected to give thecorresponding N-protected-piperidine-2(R),3(S)-dicarboxylic acid,diester derivative of structure (21) as described previously in SchemeA, step b.

In step e, the appropriate N-protected-piperidine-2(R),3(S)-dicarboxylicacid, diester derivative of structure (21) is coupled with anappropriate phosphonate ester of structure (5) to give the correspondingN-protected-3(S)-[(dialkoxyphosphinyl)acetyl]piperidine-2(R)-carboxylicacid, ester of structure (22) as described previously in Scheme A, stepd.

In step f, the N-protecting group of the appropriateN-protected-3(S)-[(dialkoxyphosphinyl)acetyl]piperidine-2(R)-carboxylicacid, ester of structure (22) is removed to give the corresponding3(S)-[(dialkoxyphosphinyl)acetyl]piperidine-2(R)-carboxylic acid, esterof structure (23a) as described previously in Scheme A, step f.

The appropriate3(S)-[(dialkoxyphosphinyl)acetyl]piperidine-2(R)-carboxylic acid, esterof structure (23a) can be further functionalized as described previouslyin Scheme A, steps g₁ -i.

The appropriate 3(S)-[(functionalizedphosphinyl)acetyl]piperidine-2(R)-carboxylic acid derivatives of FormulaI prepared as described above in Scheme D may also be furtherfunctionalized into the corresponding3(S)-[1-imino-2-phosponoethyl]piperidine-2(R)-carboxylic acidderivatives of Formula I as described previously in Scheme C, step a.

Starting materials for use in Scheme D are readily available to one ofordinary skill in the art.

The following examples present typical syntheses as described in SchemeD. These examples are intended to be illustrative only and are notintended to limit the scope of the present invention in any way.

Example 3

3(S)-[(Diethoxyphosphinyl)acetyl]piperidine-2(R)-carboxylic acid, methylester ##STR13## Step a: Pyridine-2,3-dicarboxylic acid, dimethyl ester

Dissolve pyridine-2,3-dicarboxylic acid (100 g) in methanol (1.25 L).Bubble in HCl gas until a solution is obtained. Reflux overnight,evaporate the solvent in vacuo and neutralize with saturated aqueoussodium hydrogen carbonate in ethyl acetate. Separate the organic phase,dry (MgSO₄) and evaporate the solvent in vacuo to give the titlecompound as a white solid (96.1 g).

¹ H NMR (90 MHz, CDCl₃) ppm 8.6 (m, 1), 8.05 (m, 1), 7.4 (m, 1), 3.9 (s,3), 3.8 (s, 3).

Step b: d,l-cis-Piperidine-2,3-dicarboxylic acid, dimethyl ester

Dissolve pyridine-2,3-dicarboxylic acid, dimethyl ester (19 g) inmethanol (500 mL) and treat with 20% palladium hydroxide/carbon (1.5 g).Place on a Paar Hydrogenation Apparatus and hydrogenate at 50 psi for 6hours. Filter and evaporate the solvent in vacuo to give the titlecompound (14 g).

¹ H NMR (300 MHz, CDCl₃) ppm 3.76 (s, 3), 3.70 (s, 3), 3.66 (d, 1), 3.06(m, 1), 2.99 (m, 1), 2.7 (m, 1), 2.24-2.1 (m, 2), 1.79 (m, 1), 1.5 (m,2).

Step c: Piperidine-2(R),3(S)-dicarboxylic acid, dimethyl ester andPiperidine-2(S)-carboxylic acid-3(R)-carboxylic acid, monomethyl ester

Dissolve d,l-cis-piperidine-2,3-dicarboxylic acid, dimethyl ester (75mg) in pH 7.4 phosphate buffer (1.5 mL) and shake for 24 hours in thepresence of porcine liver esterase. Evaporate to a residue, stir withethyl acetate and filter. Evaporate the solvent in vacuo to give thetitle dimethyl ester compound.

Alternatively, extract the residue with water and purify by ion-exchangechromatography to give the title monoester compound.

Step d: N-(9-Phenylfluorenyl)piperidine-2(R),3(S)-dicarboxylic acid,dimethyl ester

Dissolve piperidine-2(R),3(S)-dicarboxylic acid, dimethyl ester (5.0 g,24.8 mmol) and diisopropylethylamine (3.5 g, 41.8 mmol) in acetonitrile(90 mL) and add 4A molecular sieves. Add phenylfluorenyl bromide (8.8 g,27.3 mmol) and lead nitrate (8.2 g, 24.8 mmol). Stir at room temperatureunder an argon atmosphere Overnight. Add methylene chloride (150 mL) andfilter through celite. Wash the filtrate with saturated aqueous sodiumhydrogen carbonate (2×) and saturated sodium chloride. Dry (MgS₄),evaporate the solvent in vacuo and recrystallize (methylenechloride/hexane) to give the title compound.

Step e:N-(9-Phenylfluorenyl)-3(S)-[(diethoxyphosphinyl)acetyl]piperidine-2(R)-carboxylicacid, methyl ester

Dissolve diethyl methylphosphate (2.28 g, 15 mmol) in anhydroustetrahydrofuran (10 mL), cool to -78° C. and place under an argonatmosphere. Add, by dropwise addition, n-butyllithium (8 mL of a 1.6Msolution, 15 mmol). Stir for 20 minutes at -78° C. and add a solution ofN-(9-phenylfluorenyl)piperidine-2(R),3(S)-dicarboxylic acid, dimethylester (2.21 g, 5 mmol) in anhydrous tetrahydrofuran (5 mL). Stir for 1/2hour at -78° C., quench with acetic acid (2 mL) and warm to roomtemperature. Quench with water (50 mL) and extract into ethyl acetate(100 mL). Evaporate the solvent in vacuo to give a residue. Purify bysilica gel chromatography to give the title compound.

Step f: 3(S)-[(Diethoxyphosphinyl)acetyl]piperidine-2(R)-carboxylicacid, methyl ester

DissolveN-(9-phenylfluorenyl)-3(S)-(diethoxyphosphinyl)acetyl]piperidine-2(R)-carboxylicacid, ethyl ester (1 g) in acetonitrile (7 mL) and water (1 mL). Cool to0° C. and add, by dropwise addition, trifluoroacetic acid (7 mL). Stirat 0° C. for 1 hour then warm to room temperature over 1 hour. Extractinto ethyl acetate (10×100 mL) and evaporate the solvent in vacuo togive the title compound.

Example 4

3(S)-[(Diethoxyphosphinyl)acetyl]piperidine-4-methyl-2-(R)-carboxylicacid, methyl ester and3(R)-[(Diethoxyphosphinyl)acetyl]piperidine-4-methyl-2(S)-carboxylicacid, methyl ester ##STR14## Step a: Pyridine-4-methyl-2,3-dicarboxylicacid, dimethyl ester

Dissolve pyridine-4-methyl-2,3-dicarboxylic acid (100 g) in methanol(1.25 L). Bubble in HCl gas until a solution is obtained. Refluxovernight, evaporate the solvent in vacuo and neutralize with saturatedaqueous sodium hydrogen carbonate in ethyl acetate. Separate the organicphase, dry (MgSO₄) and evaporate the solvent in vacuo to give the titlecompound.

Step b: d,l-cis-piperidine-4-methyl-2,3-dicarboxylic acid dimethyl ester

Dissolve pyridine-4-methyl-2,3-dicarboxylic acid, dimethyl ester (19 g)in methanol (500 mL) and treat with 20% palladium hydroxide/carbon (1.5g). Place on a Paar Hydrogenation Apparatus and hydrogenate at 50 psifor 6 hours. Filter and evaporate the solvent in vacuo to give the titlecompound.

Step c: Piperidine-4-methyl-2(R),3(S)-dicarboxylic acid, dimethyl esterand Piperidine-4-methyl-2(R)-carboxylic acid-3(S)-carboxylic acid,monomethyl ester and Piperidine-4-methyl-2(S),3(R)-dicarboxylic acid,dimethyl ester and Piperidine-4-methyl-2(S)-carboxylicacid-3(R)-carboxylic acid, monomethyl ester

Dissolve d,l-cis-piperidine-4-methyl-2,3-dicarboxylic acid, dimethylester (75 mg) in pH 7.4 phosphate buffer (1.5 mL) and shake for 24 hoursin the presence of porcine liver esterase. Evaporate to a residue, stirwith ethyl acetate and filter. Evaporate the solvent in vacuo to givethe title diester compounds.

Alternatively, extract the residue with water and purify by ion-exchangechromatography to give the title monoester compounds.

step d: N-(9-Phenylfluorenyl)piperidine-4-methyl-2(R),3(S)-dicarboxylicacid dimethyl ester andN-(9-Phenylfluorenyl)piperidine-4-methyl-2(S),3(R)-dicarboxylic acid,dimethyl ester

Dissolve the mixture of piperidine-4-methyl-2(R),3(S)-dicarboxylic acid,dimethyl ester and piperidine-4-methyl-2(S),3(R)-dicarboxylic acid,dimethyl ester (5.33 g, 24.8 mmol) and diisopropylethylamine (3.5 g,41.8 mmol) in acetonitrile (90 mL). Add phenylfluorenyl bromide (8.8 g,27.3 mmol) and lead nitrate (8.2 g, 24.8 mmol). Stir at room temperatureunder an argon atmosphere overnight. Add methylene chloride (150 mL) andfilter through celite. Wash the filtrate with saturated aqueous sodiumhydrogen carbonate (2×) and saturated sodium chloride. Dry (MgSO₄),evaporate the solvent in vacuo and purify by silica gel chromatographyto give the title compound.

Step e:N-(9-Phenylfluorenyl)-3(S)-[(diethoxyphosphinyl)acetyl]piperidine-4-methyl-2(R)-carboxylicacid, methyl ester andN-(9-Phenylfluorenyl)-3(R)-[(diethoxyphosphinyl)acetyl]piperidine-4-methyl-2(S)-carboxylicacid, methyl ester

Dissolve diethyl methylphosphate (2.28 g, 15 mmol) in anhydroustetrahydrofuran (10 mL), cool to -78° C. and place under an argonatmosphere. Add, by dropwise addition, n-butyllithium (8 mL of a 1.6Msolution, 15 mmol). Stir for 20 minutes at -78° C. and add a solution ofthe mixture ofN-(9-phenylfluorenyl)piperidine-4-methyl-2(R),3(S)-dicarboxylic acid,dimethyl esterN-(9-phenylfluorenyl)piperidine-4-methyl-2(S),3(R)-dicarboxylic acid,dimethyl ester (2.35 g, 5 mmol) in anhydrous tetrahydrofuran (5 mL).Stir for 1/2 hour at -78° C., quench with acetic acid (2 mL) and warm toroom temperature. Quench with water (50 mL) and extract into ethylacetate (100 mL). Evaporate the solvent in vacuo to give a residue.Purify by silica gel chromatography to give the title compounds.

Step f:3(S)-[(Diethoxyhosphinyl)acetyl]piperidine-4-methyl-2(R)-carboxylicacid, methyl ester and3(R)-[(Diethoxyphosphinyl)acetyl]piperidine-4-methyl-2(S)-carboxylicacid, methyl ester

Dissolve the mixture ofN-(9-phenylfluorenyl)-3(S)-[(diethoxyphosphinyl)acetyl]piperidine-4-methyl-2(R)-carboxylicacid, methyl esterN-(9-phenylfluorenyl)-3(R)-[(diethoxyphosphinyl)acetyl]piperidine-4-methyl-2(S)-carboxylicacid, methyl ester (1 g) in acetonitrile (7 mL) and water (1 mL). Coolto 0° C. and add, by dropwise addition, trifluoroacetic acid (7 mL).Stir at 0° C. for 1 hour then warm to room temperature over 1 hour.Extract into ethyl acetate (10×100 mL) and evaporate the solvent invacuo to give the title compound.

Example 5

3(S)-(Phosphonoacetyl]piperidine-4-methyl-2(R)-carboxylic acid and 3(R)-(Phosphonoacetyl]piperidine-4-methyl-2(S)-carboxylic acid ##STR15##

Dissolve the mixture of3(S)-[(diethoxyphosphinyl)acetyl]piperidine-4-methyl-2(R)-carboxylicacid, methyl ester and3(R)-[(diethoxyphosphinyl)acetyl]piperidine-4-methyl-2(S)-carboxylicacid, methyl ester (3 g) in acetonitrile (20 mL) and methylene chloride(20 mL). Add trimethylsilyl iodide (3.5 mL, 24 mmol) and stir for 5hours. Pour into water (250 mL) and wash with toluene (3×250 mL). Freezedry the aqueous phase to give a solid residue. Take up the solid residuein methanol (10 mL) and isopropanol (5 mL). Add propylene oxide (2 mL)and stir for 1 hour. Filter to give the title compound.

Example 6

3(S)-[(Diethoxyphosphinyl)acetyl]piperidine-5-methyl-2(R)-carboxylicacid, methyl ester ##STR16##

Step a: Pyridine-5-methyl-2,3-dicarboxylic acid, dimethyl ester

Dissolve pyridine-5-methyl-2,3-dicarboxylic acid (100 g) in methanol(1.25 L). Bubble in HCl gas until a solution is obtained. Refluxovernight, evaporate the solvent in vacuo and neutralize with saturatedaqueous sodium hydrogen carbonate in ethyl acetate. Separate the organicphase, dry (MgSO₄) and evaporate the solvent in vacuo to give the titlecompound.

Step b: d,l-cis-Piperidine-5-methyl-2,3-dicarboxylic acid, dimethylester

Dissolve pyridine-5-methyl-2,3-dicarboxylic acid, dimethyl ester (19 g)in methanol (500 mL) and treat with 20% palladium hydroxide/carbon (1.5g). Place on a Paar Hydrogenation Apparatus and hydrogenate at 50 psifor 6 hours. Filter and evaporate the solvent in vacuo to give the titlecompound.

Step c: Piperidine-5-methyl-2(R),3(S)-dicarboxylic acid, dimethyl esterand Piperidine-5-methyl-2(R)-carboxylic acid-3(S)-carboxylic acid,monomethyl ester

Dissolve d,l-cis-piperidine-5-methyl-2,3-dicarboxylic acid, dimethylester (75 mg) in pH 7.4 phosphate buffer (1.5 mL) and shake for 24 hoursin the presence of porcine liver esterase. Evaporate to a residue, stirwith ethyl acetate and filter. Evaporate the solvent in vacuo to givethe title compound.

Alternatively, extract the residue with water and purify by ion-exchangechromatography to give the title monoester compounds.

Step d: N-(9-Phenylfluorenyl)piperidine-5-methyl-2(R),3(S)-dicarboxylicacid, dimethyl ester

Dissolve piperidine-5-methyl-2(R),3(S)-dicarboxylic acid, dimethyl ester(5.33 g, 24.8 mmol) and diisopropylethylamine (3.5 g, 41.8 mmol) inacetonitrile (90 mL). Add phenylfluorenyl bromide (8.8 g, 27.3 mmol) andlead nitrate (8.2 g, 24.8 mmol). Stir at room temperature under an argonatmosphere overnight. Add methylene chloride (150 mL) and filter throughcelite. Wash the filtrate with saturated aqueous sodium hydrogencarbonate (2×) and saturated sodium chloride. Dry (MgSO₄), evaporate thesolvent in vacuo and purify by silica gel chromatography to give thetitle compound.

Step e:N-(9-Phenylfluorenyl)-3(S)-[(diethoxyphosphinyl)acetyl]piperidine-5-methyl-2(R)-carboxylicacid, methyl ester

Dissolve diethyl methylphosphate (2.28 g, 15 mmol) in anhydroustetrahydrofuran (10 mL), cool to -78° C and place under an argonatmosphere. Add, by dropwise addition, n-butyllithium (8 mL of a 1.6Msolution, 15 mmol). Stir for 20 minutes at -78° C. and add a solution ofN-(9-phenylfluorenyl)piperidine-5-methyl-2(R),3(S)-dicarboxylic acid,dimethyl ester (2.35 g, 5 mmol) in anhydrous tetrahydrofuran (5 mL).Stir for 1/2 hour at -78° C., quench with acetic acid (2 mL) and warm toroom temperature. Quench with water (50 mL) and extract into ethylacetate (100 mL). Evaporate the solvent in vacuo to give a residue.Purify by silica gel chromatography to give the title compound.

Step f:3(S)-[(Diethoxyphosphinyl)acetyl]piperidine-5-methyl-2(R)-carboxylicacid, methyl ester

DissolveN-(9-phenylfluorenyl)-3(S)-[(diethoxyphosphinyl)acetyl]piperidine-5-methyl-2(R)-carboxylicacid, methyl ester (1 g) in acetonitrile (7 mL) and water (1 mL). Coolto 0° C. and add, by dropwise addition, trifluoroacetic acid (7 mL).Stir at 0° C. for 1 hour then warm to room temperature over 1 hour.Extract into ethyl acetate (10×100 mL) and evaporate the solvent invacuo to give the title compound.

Example 7

3(S)-(Phosphonoacetyl)piperidine-5-methyl-2(R)-carboxylic acid ##STR17##

Dissolve the mixture of3(S)-[(diethoxyphosphinyl)acetyl]piperidine-5-methyl-2(R)-carboxylicacid, methyl ester (3 g) in acetonitrile (20 mL) and methylene chloride(20 mL). Add trimethylsilyl iodide (3.5 mL, 24 mmol) and stir for 5hours. Pour into water (250 mL) and wash with toluene (3×250 mL). Freezedry the aqueous phase to give a solid residue. Take up the solid residuein methanol (10 mL) and isopropanol (5 mL). Add propylene oxide (2 mL)and stir for 1 hour. Filter and dry to give the title compound.

An alternative synthetic procedure for preparing the d,l-cis or theenatiomerically pure 2(R),3(S) and 2(S),3(R) saturated piperidinecompounds of Formula I wherein R₅ is represented by hydrogen isdescribed in Scheme E. In Scheme E all substituents unless otherwiseindicated are as previously defined. ##STR18##

Scheme E provides an alternative general synthetic procedure forpreparing the d,l-cis or the enatiomerically pure 2(R),3(S) and2(S),3(R) saturated piperidine compounds of Formula I wherein R₅ isrepresented by hydrogen.

In step a, the appropriate d,l-cis-piperidine-2,3-dicarboxylic acid,diester derivative of structure (19) is protected to give thecorresponding d,l-cis-N-protected-piperidine-2,3-dicarboxylic acid,diester derivative of structure (24) as described previously in SchemeA, step b.

In step b, the appropriated,l-cis-N-protected-piperidine-2,3-dicarboxylic acid, diester derivativeof structure (24) is coupled with the appropriate phosphonate ester ofstructure (5) to give the correspondingd,l-cis-N-protected-3-[(dialkoxyphosphinyl)acetyl]piperidine-2-carboxylicacid, ester of structure (25) as described previously in Scheme A, stepd.

In step c, the appropriated,l-cis-N-protected-3-[(dialkoxyphosphinyl)acetyl]piperidine-2-carboxylicacid, ester of structure (25) is deprotected to give the correspondingd,l-cis-3-[(dialkoxyphosphinyl)acetyl]piperidine-2-carboxylic acid,ester of structure (26) as described previously in Scheme A, step f.

In optional step d, the appropriated,l-cis-3-[(dialkoxyphosphinyl)acetyl]piperidine-2-carboxylic acid,ester of structure (26) is separated to give the corresponding3(S)-[(dialkoxyphosphinyl)acetyl]piperidine-2(R)-carboxylic acid ofstructure (27) and the3(R)-[(dialkoxyphosphinyl)acetyl]piperidine-2(S)-carboxylic acid, esterof structure (23b) as described previously in Scheme D, step c.

The appropriate 3(S)-[(dialkoxyphosphinyl)acetyl]piperidine-2(R)-carboxylic acid of structure (27) can be further functionalized asdescribed previously in Scheme A, steps g₁ and steps h₁ -i.

The appropriate3(R)-[(dialkoxyphosphinyl)acetyl]piperidine-2(S)-carboxylic acid, esterof structure (23b) can be further functionalized as described previouslyin Scheme A, steps g₁ -i.

The appropriate d,l-cis-3-[(functionalizedphosphinyl)acetyl]piperidine-2-carboxylic acid derivatives,3(S)-[(functionalized phosphinyl)acetyl]piperidine-2(R)-carboxylic acidderivatives and 3(R)-[(functionalizedphosphinyl)acetyl]piperidine-2(S)-carboxylic acid derivatives of FormulaI prepared as described above in Scheme E may also be furtherfunctionalized into the correspondingd,l-cis-3-[1-imino-2-phosponoethyl]piperidine-2-carboxylic acidderivatives, 3(S)-[1-imino-2-phosponoethyl-]piperidine-2(R)-carboxylicacid derivatives and3(R)-[1-imino-2-phosponoethyl]piperidine-2(S)-carboxylic acidderivatives of Formula I as described previously in Scheme C, step a.

Starting materials for use in Scheme E are readily available to one ofordinary skill in the art.

The following examples present typical syntheses as described in SchemeE. These examples are intended to be illustrative only and are notintended to limit the scope of the present invention in any way.

Example 8

d,l-cis-3-[(Diethoxyphosphinyl)acetyl]piperidine-2-carboxylic acid,methyl ester ##STR19## Step a:d,l-cis-N-(9-Phenylfluorenyl)piperidine-2,3-dicarboxylic acid diethylester

Dissolve d,l-cis-piperidine-2,3-dicarboxylic acid, diethyl ester (5.0 g,24.8 mmol) and diisopropylethylamine (3.5 g, 41.8 mmol) in acetonitrile(90 mL). Add phenylfluorenyl bromide (8.8 g, 27.3 mmol) and lead nitrate(8.2 g, 24.8 mmol). Stir at room temperature under an argon atmosphereovernight. Add methylene chloride (150 mL) and filter through celite.Wash the filtrate with saturated aqueous sodium hydrogen carbonate (2×)and saturated sodium chloride. Dry (MgSO₄) and evaporate the solvent invacuo to give 12.5 g red foam. Purify by silica gel chromatography (9:1hexane/ethyl ether to 7:3 hexane/ethyl ether) to give the title compoundas a white solid (8.7 g); mp 177°-177.5° C. (hexane/ethyl ether).

Step b:d,l-cis-N-(9-Phenylfluorenyl)-3-[(diethoxyphosphinyl)acetyl]piperidine-2-carboxylicacid, ethyl ester

Dissolve diethyl methylphosphate (2.28 g, 15 mmol) in anhydroustetrahydrofuran (10 mL), cool to -78° C. and place under an argonatmosphere. Add, by dropwise addition, n-butyllithium (8 mL of a 1.6Msolution, 15 mmol). Stir for minutes at -78° C. and add a solution ofd,l-cis-N-(9-phenylfluorenyl)piperidine-2,3-dicarboxylic acid, diethylester (2.21 g, 5 mmol) in anhydrous tetrahydrofuran (5 mL). Stir for 1/2hour at -78° C., quench with acetic acid (2 mL) and warm to roomtemperature. Quench with water (50 mL) and extract into ethyl acetate(100 mL). Evaporate the solvent in vacuo to give a residue.Recrystallize the residue (ethyl acetate) to give 0.8 g of a whitesolid. Purify by silica gel chromatography (ethyl acetate) to give thetitle compound (0.5 g).

¹ H NMR (300 MHz, CDCl₃) ppm 7.69 (dd, 2), 7.15-7.45 (m, 9), 4.1 (m, 4),3.78 (d, ?), 3.49 (dt, 1), 2.95-3.3 (m, 4), 2.85 (s, 3), 1.7-2.15 (m,4), 1.3 (m, 6).

Step c: d,l-cis-3-[(Diethoxyphosphinyl)acetyl]piperidine-2-carboxylicacid, ethyl ester

Dissolved,l-cis-N-(9-phenylfluorenyl)-3-[(diethoxyphosphinyl)acetyl]piperidine-2-carboxylicacid, ethyl ester (1 g) in acetonitrile (7 mL) and water (1 mL). Cool to0° C. and add, by dropwise addition, trifluoroacetic acid (7 mL). Stirat 0° C. for 1 hour then warm to room temperature over 1 hour. Extractinto ethyl acetate (10×100 mL) and evaporate the solvent in vacuo togive the title compound.

¹ H NMR (300 MHz, CDCl₃) ppm 4.15 (m, 4), 3.71 (m, 1), 3.69 (s, 3),2.9-3.4 (m, 4), 2.70 (m, 1), 1.9-2.2 (m, 4), 1.5 (m, 2), 1.32 (m, 6).

An alternative synthetic procedure for preparing the enantiomericallypure 2(R),3(S) saturated piperidine compounds of Formula I wherein R₅ isrepresented by hydrogen is set forth in Scheme F. In Scheme F, allsubstituents unless otherwise indicated are as previously defined.##STR20##

Scheme F provides an alternative general synthetic procedure forpreparing the enantiomerically pure 2(R),3(S) saturated piperidinecompounds of Formula I wherein R₅ is represented by hydrogen.

In step a, D-aspartic acid (28) is protected to give the correspondingβ-methyl-D-aspartate (29) as described previously in Scheme D, step a.

In step b, β-methyl-D-aspartate (29) is protected to give thecorresponding α-C₁ -C₄ alkyl or benzyl-β-methyl-D-aspartate acetic acidof structure (30) with the tert-butyl ester being preferred.

For example, β-methyl-D-aspartate (29) is contacted with a molar excessof tert-butyl acetate and a slight molar excess of an appropriate acidsuch as perchloric acid. The reactants are typically stirred together atroom temperature for a period of time ranging from 1-24 hours. Theα-tert-butyl-β-methyl-D-aspartate acetic acid of structure (30) isrecovered from the reaction zone by extractive methods as is known inthe art.

In step c, the appropriate α-C₁ -C₄ alkyl or benzyl-β-methyl-D-aspartateacetic acid of structure (30) is alkylated with the appropriate1-bromo-3-chloropropane of structure (31) to give the corresponding α-C₁-C₄ alkyl or benzyl-β-methyl-N-(3-chloropropyl)-D-aspartate of structure(32).

For example, the appropriate α-C₁ -C₄ alkyl orbenzyl-β-methyl-D-aspartate acetic acid of structure (30) is contactedwith a molar equivalent of an appropriate 1-bromo-3-chloropropane ofstructure (31) and a molar excess of an appropriate base such astriethylamine. The reactants are typically contacted in a suitableorganic solvent such as acetonitrile. The reactants are typicallystirred together for a period of time ranging from 2-24 hours and at atemperature range of from room temperature to 80° C. The α-C₁ -C₄ alkylor benzyl-β-methyl-N-(3-chloropropyl)-D-aspartate of structure (32) isrecovered from the reaction zone by extractive methods as is known inthe art. It may be purified by silica gel chromatography.

The appropriate 1-bromo-3-chloropropane of structure (31) is one inwhich R₃ is the same as is desired in the final product.

In step d, the appropriate α-C₁ -C₄ alkyl orbenzyl-β-methyl-N-(3-chloropropyl)-D-aspartate of structure (32) isprotected to give the corresponding α-C₁ -C₄ alkyl orbenzyl-β-methyl-N-(3-chloropropyl)-N-(9-phenylfluorenyl)-D-aspartate ofstructure (33) as described previously in Scheme A, step b.

In step e, the chloride functionality of the appropriate α-C₁ -C₄ alkylor benzyl-β-methyl-N-(3-chloropropyl)-N-(9-phenylfluorenyl)-D-aspartateof structure (33) is exchanged to give the corresponding α-C₁ -C₄ alkylor benzyl-β-methyl-N(-3-iodopropyl)-N-(9-phenylfluorenyl)-D-aspartate ofstructure (34).

For example, the appropriate α-C₁ -C₄ alkyl orbenzyl-β-methyl-N-(3-chloropropyl)-N-(9-phenylfluorenyl)-D-aspartate ofstructure (33) is contacted with a molar excess of an iodide source,such as sodium iodide. The reactants are typically contacted in asuitable organic solvent such as acetonitrile. The reactants aretypically stirred together for a period of time ranging from 2-24 hoursand at a temperature range of from room temperature to 65° C. The α-C₁-C₄ alkyl orbenzyl-β-methyl-N-(3-iodopropyl)-N-(9-phenylfluorenyl)-D-aspartate ofstructure (34) is recovered from the reaction zone by extractive methodsas is known in the art. It may be purified by recrystallization.

In step f, the appropriate α-C₁ -C₄ alkyl orbenzyl-β-methyl-N-(3-iodopropyl)-N-(9-phenylfluorenyl)-D-aspartate ofstructure (34) is cyclized to give the correspondingN-protected-piperidine-2(R)-C₁ -C₄ alkyl or benzyl ester-3(S)-methylester of structure (35).

For example, the appropriate α-C₁ -C₄ alkyl orbenzyl-β-methyl-N-(3-iodopropyl)-N-(9-phenylfluorenyl)-D-aspartate ofstructure (34) is contacted with an appropriate base such as lithiumdiisopropylamine. The reactants are typically contacted in a suitableorganic solvent such as tetrahydrofuran. The reactants are typicallystirred together for a period of time ranging from 2-20 hours and at atemperature range of from -78° C. to -20° C. TheN-protected-piperidine-2(R)-C₁ -C₄ alkyl or benzyl ester-3(S)-methylester of structure (35) is recovered from the reaction zone by alow-temperature quench into an appropriate proton source, such asdiisopropyl phenol, followed by acidification and extraction as is knownin the art. It may be purified by silica gel chromatography.

In step g, the appropriate N-(9-phenylfluorenyl)piperidine-2(R)-C₁ -C₄alkyl or benzyl ester-3(S)-methyl ester of structure (35) is coupledwith an appropriate phosphonate ester of structure (5) to give thecorrespondingN-(9-phenylfluorenyl)-3(S)-[(dialkoxyphosphinyl)acetyl]piperidine-2(R)-carboxylicacid, benzyl or C₁ -C₄ alkyl ester of structure (36) as describedpreviously in Scheme A, step d.

In step h, the appropriateN-(9-phenylfluorenyl)-3(S)-[(dialkoxyphosphinyl)acetyl]piperidine-2(R)-carboxylicacid, benzyl or C₁ -C₄ alkyl ester of structure (36) is deprotected togive the corresponding3(S)-[(dialkoxyphosphinyl)acetyl]piperidine-2(R)-carboxylic acid, benzylor C₁ -C₄ alkyl ester of structure (37) as described previously inScheme A, step f.

The appropriate3(S)-[(dialkoxyphosphinyl)acetyl]piperidine-2(R)-carboxylic acid, benzylor C₁ -C₄ alkyl ester of structure (37) can be further functionalized asdescribed previously in Scheme A, steps g₁ -i.

The appropriate 3(S)-[(functionalizedphosphinyl)acetyl]piperidine-2(R)-carboxylic acid derivatives of FormulaI prepared as described above in Scheme F may also be furtherfunctionalized into the corresponding3(S)-[1-imino-2-phosponoethyl]piperidine-2(R)-carboxylic acidderivatives of Formula I as described previously in Scheme C, step a.

Alternatively, the enantiomerically pure 2(S),3(R) saturated piperidinecompounds of Formula I wherein R₅ is represented by hydrogen can beprepared as set forth in Scheme F by substituting L-aspartic acid forthe D-aspartic acid (28).

Starting materials for use in Scheme F are readily available to one ofordinary skill in the art.

The following examples present typical syntheses as described in SchemeF. These examples are intended to be illustrative only and are notintended to limit the scope of the present invention in any way.

Example 9

3(S)-(Phosphonoacetyl)piperidine-2 (R)-carboxylic acid ##STR21## Step a:β-Methyl-D-aspartate hydrochloride

Cool methanol (525 mL) to -20° C. and place under an atmosphere ofnitrogen. Add, by dropwise addition, thionyl chloride (80 mL). AddD-aspartic acid (100 g, 0.75 mol) in one portion and allow the reactionto warm to room temperature over approximately 1 hour. Stir for 50minutes at room temperature and pour into anhydrous ethyl ether (1.5 L).Filter the resulting solid, dissolve partly in warm ethanol (500 mL) andfilter again. Add the filtrated to ethyl ether (1.5 L) and filter theresulting solid. Dry to give the title compound (85.3 g, 62%).

¹ H NMR (300 MHz, CDCl₃) ppm 4.22 (t, 1), 3.67 (s, 3), 2.96 (dd, 2).

Step b: α-tert-Butyl-β-methyl-D-aspartate acetic acid

Suspend β-methyl-D-aspartate hydrochloride (40 g, 0.22 mol) intert-butyl acetate (1.5 L) and add perchloric acid (20.7 mL of a 20%solution, 0.24 mol). Stir at room temperature under an atmosphere ofargon for 3 hours. Pour into saturated sodium hydrogen carbonate and addsolid sodium hydrogen carbonate until the mixture is basic. Add ethylether and separate the organic phase. Extract the aqueous phases withethyl ether, combine the organic phases and dry (MgSO₄). Evaporate thesolvent in vacuo to give the title compound as a clear oil (34 g).

¹ H NMR (300 MHz, CDCl₃) ppm 5.64 (bs, 3), 3.78 (dd, 1), 3.76 (s, 3),2.8 (m, 2), 2.04 (s, 3), 1.46 (s, 9).

Step c: α-tert-Butyl-β-methyl-N-(3-chloropropyl)-D-aspartate

Mix α-tert-butyl-β-methyl-D-aspartate acetic acid (36 g, 0.196 mol),1-bromo-3-chloropropane (90 g), triethylamine (40 g) and acetonitrile(150 mL). Heat at 80° C. and stir for 16 hours. Evaporate the solvent togive a residue. Take up the residue in ethyl acetate (250 mL) and washwith brine (100 mL), saturated sodium hydrogen carbonate (100 mL) andbrine (100 mL). Dry (Na₂ SO₄) and evaporate the solvent in vacuo. Purifyby silica gel chromatography (1:1 ethyl acetate/hexane) to give thetitle compound (32 g).

¹ H NMR (90 MHz, CDCl₃) ppm 3.74 (s, 3), 3.6 (m, 2), 2.8 (m, 1), 2.65(m, 2), 1.9 (m, 2), 1.5 (s, 9).

Step d:α-tert-Butyl-β-methyl-N-(3-chloropropyl)-N-(9-phenylfluorenyl)-D-aspartate

Add α-tert-butyl-β-methyl-N-(3-chloropropyl)-D-aspartate 24.8 g, 88.6mmol) to anhydrous acetonitrile (150 mL) and place under a nitrogenatmosphere. Stir vigorously and add lead nitrate (24.8 g, 74.8 mmol).Simultaneously add, by dropwise addition over 5 hours, a solution of9-phenylfluorenyl bromide (32 g, 99.6 mmol) in chloroform (100 mL) and asolution of diisopropylethylamine (20.4 mL, 117 mmol) in acetonitrile.Stir overnight at room temperature. Add methylene chloride (250 mL),filter and add methylene chloride (300 mL) to the filtrate. Wash withsaturated sodium hydrogen carbonate (2×250 mL), brine (1×250 mL) andsaturated sodium hydrogen carbonate (1×250 mL). Dry (Na₂ SO₄) andevaporate to a residue. Purify by silica gel chromatography (10% hexanein methylene chloride) to give the title compound (26 g).

¹ H NMR (300 MHz, CDCl₃) ppm 7.2-7.7 (m, 13), 3.79 (dd, 1), 3.6-3.4 (m,2), 3.48 (s, 3), 3.2 (m, 1), 2185 (m, 1), 2.62 (dd, 1), 1.85-2.1 (m, 2),1.8 (m, dd), 1.43 (s, 9).

Step e:α-tert-Butyl-β-methyl-N-(3-iodopropyl)-N-(9-phenylfluorenyl)-D-aspartate

Mixα-tert-butyl-β-methyl-N-(3-chloropropyl)-N-(9-phenylfluorenyl)-D-aspartate(26 g, 0.05 mol), sodium iodide (50 g) and anhydrous acetonitrile (250mL). Place under a nitrogen atmosphere and stir at 65° C. for 16 hours.Cool and add methylene chloride (250 mL). Filter and evaporate thesolvent to a residue. Take up the residue in methylene chloride (300mL), wash with water (100 mL), 5% sodiumthiosulphate (100 mL), water(100 mL) and brine (100 mL). Dry (Na₂ SO₄) and evaporate to a residue.Recrystallize (ethyl ether) to give the title compound (21.5 g).

¹ H NMR (300 MHz, CDCl₃) ppm 7.2-7.8 (m, 13), 3.79 (dd, 1), 3.48 (s, 3),2.95-3.2 (m, 3), 2.88 (m, 1), 1.8-2.3 (m, 2), 1.79 (dd, 1), 1.43 (s, 9).

Step f: N-(9-Phenylfluorenyl)-piperidine-2(R)-tert-butyl-3(S)-methylester

Dissolve diisopropylamine (12 mL, 85.6 mmol) in anhydroustetrahydrofuran, cool to -78° C. and place under an inert atmosphere.Add n-butyllithium (52 mL of a 1.6M solution in hexane, 83.2 mmol) andstir at -78° C. for 20 minutes. Add, by dropwise addition, a solution ofα-tert-butyl-β-methyl-N-(3-iodopropyl)-N-(9-phenylfluorenyl)-D-aspartate(20 g, 32.7 mmol) in anhydrous tetrahydrofuran (50 mL). Stir at -78° C.for 1 hour, warm to -38° C. and stir for 3 hours. Cool to -78° C. andtransfer via cannula to a -78° C. solution of diisopropyl phenol (30.8g, 0.17 mol) in tetrahydrofuran (200 mL). Stir for 1 hour and add addacetic acid (5.2 mL). Warm to room temperature and quench with water(100 mL). Partition between methylene chloride (500 mL) and water (300mL). Separate the organic phase, dry (Na₂ SO₄) and evaporate to aresidue. Purify by silica gel chromatography (10% hexane in methylenechloride) to give the title compound (13.8 g).

¹ H NMR (CDCl₃) ppm 7.2-7.8 (m, 13), 3.82 (d, 1), 3.69 (td, 1), 3.55 (s,3), 3.11 (m, 1), 2.91 (m, 1), 2.08 (m, 1), 1.6-1.9 (m, 2), 1.31 (m, 1),1.03 (m, 9).

Step g:N-(9-Phenylfluorenyl)-3(S)-[(diethoxyphosphinyl)acetyl]piperidine-2(R)-carboxylicacid tert-butyl ester

Dissolve diethyl methylphosphate (0.57 g) in anhydrous tetrahydrofuran(10 mL), cool to -78° C. and place under an argon atmosphere. Add, bydropwise addition, n-butyllithium (2.34 mL of a 1.6M solution). Stir for20 minutes at -78° C. and add a solution ofN-(9-phenylfluorenyl)-piperidine-2(R)-tert-butyl-3(S)-methyl ester (0.6g, 1.24 mmol) in anhydrous tetrahydrofuran (10 mL). Stir for 2 hours at-78° C., quench with acetic acid (1 mL) and warm to room temperature.Pour into ethyl acetate (100 mL) and wash with brine (100 mL) andaqueous sodium hydrogen caronate (100 mL). Evaporate the a residue andpurify by silica gel chromatography (ethyl acetate) to give the titlecompound (0.45 g).

¹ H NMR (300 MHz, CDCl₃) ppm 7.2-7.8 (m, 13), 4.13 (m, 4), 3.79 (d, 1),3.73 (m, 1), 3.23 (m, 1), 3.09 (m, 1), 3.03 (dd, 1).

Step h: 3(S)-(Phosphonoacetyl)piperidine-2(R)-carboxylic acid

Mix trifluoroacetic acid (30 mL) with acetonitrile (10 mL) and add, bydropwise addition, to an ice-cold solution ofN-(9-phenylfluorenyl)-3(S)-[(diethoxyphosphinyl)acetyl]piperidine-2(R)-carboxylicacid, tert-butyl ester (3.5 g, 5.8 mmol) in acetonitrile (40 mL) andwater (4 mL). Stir for 15 minutes, warm to room temperature and stir foran additional hour. Pour into saturated aqueous sodium hydrogencarbonate (500 mL) and extract into ethyl acetate (3×200 mL). Evaporateto a residue and take up the residue in acetonitrile (20 mL) andmethylene chloride (20 mL). Place under a nitrogen atmosphere and addtrimethylsilyl chloride (5 mL, 35 mmol). Stir overnight then add water.Stir for 15 minutes then blow to a residue with a stream of drynitrogen. Take up the residue in water (100 mL) and wash with toluene(5×100 mL). Freeze dry to give a residue. Take up the residue inmethanol (10 mL) and isopropanol (5 mL). Add propylene oxide (5 mL) andfilter to give the title compound.

¹ H NMR (300 MHz, D₂ O) ppm 3.88 (d, 1), 3.73 (m, 1), 3.41 (m, 1), 3.14(dd, 2), 3.01 (m, 1), 2.87 (m, 1), 1.98 (m, 1), 1.82 (m, 1), 1.55 (m,1).

The following compounds can be prepared in a similar fashion to thatdescribed above in Example 9:

3(S)-(Phosphonoacetyl)piperidine-5-methyl-2(R)-carboxylic acid;

3(S)-(Phosphonoacetyl]piperidine-5-benzyl-2(R)-carboxylic acid.

An alternative synthetic procedure for preparing the enatiomericallypure 2(R),3(R) saturated piperidine compounds of Formula I wherein R₅ isrepresented by hydrogen is set forth in Scheme G. In Scheme G, allsubstituents unless otherwise indicated are as previously defined.##STR22##

Scheme G provides an alternative synthetic procedure for preparing theenatiomerically pure 2(R),3(R) saturated piperidine compounds of FormulaI wherein R₅ is represented by hydrogen.

In step a, the appropriate α-C₁ -C₄ alkyl orbenzyl-β-methyl-N-(3-iodopropyl)-N-(9-phenylfluorenyl)-D-aspartate ofstructure (34) is cyclized to give the correspondingN-(9-phenylfluorenyl)-piperidine-2(R)-C₁ -C₄ alkyl or benzylester-3(R)-methyl ester of structure (38) as described previously inScheme F, step f.

In step b, the appropriate N-(9-phenylfluorenyl)piperidine-2(R)-C₁ -C₄alkyl or benzyl ester-3(R)-methyl ester of structure (38) is coupledwith the appropriate phosphonate ester of structure (5) to give thecorrespondingN-(9-phenylfluorenyl)-3(R)-[(dialkoxyphosphinyl)acetyl]piperidine-2(R)-carboxylicacid, benzyl or C₁ -C₄ alkyl ester of structure (39) as describedpreviously in Scheme A, step d.

In step c, the appropriateN-(9-phenylfluorenyl)-3(R)-[(dialkoxyphosphinyl)acetyl]piperidine-2(R)-carboxylicacid, benzyl or C₁ -C₄ alkyl ester of structure (39) is deprotected togive the corresponding3(R)-[(dialkoxyphosphinyl)acetyl]piperidine-2(R)-carboxylic acid, benzylor C₁ -C₄ alkyl ester of structure (40) as described previously inScheme A, step f.

The appropriate3(R)-[(dialkoxyphosphinyl)acetyl]piperidine-2(R)-carboxylic acid, benzylor C₁ -C₄ alkyl ester of structure (40) can be further functionalized asdescribed previously in Scheme A, steps g₁ -i.

The appropriate 3-[(functionalizedphosphinyl)acetyl]piperidine-2-carboxylic acid derivatives of Formula Iprepared as described above in Scheme G may also be furtherfunctionalized into the corresponding3(R)-[1-imino-2-phosponoethyl]piperidine-2(R)-carboxylic acidderivatives of Formula I as described previously in Scheme C, step a.

Alternatively, the enantiomerically pure 2(S),3(S) saturated piperidinecompounds of Formula I wherein R₅ is represented by hydrogen can beprepared as set forth in Scheme G by substituting α-C₁ -C₄ alkyl orbenzyl-β-methyl-N(-3-iodopropyl)-N-(9-phenylfluorenyl)-L-aspartate forαC₁ -C₄ alkyl orbenzyl-β-methyl-N-(3-iodopropyl)-N-(9-phenylfluorenyl)-D-aspartate ofstructure (34). The appropriate α-C₁ -C₄ alkyl orbenzyl-β-methyl-N-(3-iodopropyl)-N-(9-phenylfluorenyl)-L-aspartate canbe prepared as set forth in Scheme F by substituting L-aspartic acid forthe D-aspartic acid (28).

Starting materials for use in Scheme G are readily available to one ofordinary skill in the art.

The following examples present typical syntheses as described in SchemeG. These examples are intended to be illustrative only and are notintended to limit the scope of the present invention in any way.

Example 10

3(R)-(Phosphonoacetyl)piperidine-2(R)-carboxylic acid, methyl ester##STR23## Step a:N-(9-Phenylfluorenyl)-piperidine-2(R)-tert-butyl-3(R)-methyl ester

Dissolve diisopropylamine (0.6 mL, 4.3 mmol) in tetrahydrofuran (10 mL)and cool to 0° C. Add, by dropwise addition, n-butyllithium (2.7 mL of a1.6M solution, 4.3 mmol). Stir for 1/2 hour, cool to -78° C. and add, bydropwise addition, a solution ofα-tertbutyl-β-methyl-N-(3-iodopropyl)-N-(9-phenylfluorenyl)-D-aspartate(1 g, 1.6 mmol) in tetrahydrofuran (10 mL). Stir for 1 hour at -78° C.and then for 3 hours at -30° C. Transfer rapidly, via water heatedcannula, to a -78° C. solution of acetic acid in tetrahydrofuran (10mL). Allow to warm to room temperature overnight. Add ethyl acetate andwash with brine. Evaporate to a residue and purify by silica gelchromatography (50:50 to 75:25 methylene chloride/hexane) to give thetitle compound (0.35 g).

Step b:N-(9-Phenylfluorenyl)-3(R)-[(diethoxyphosphinyl)acetyl]piperidine-2(R)-carboxylicacid, tert-butyl ester

Dissolve diethyl methylphosphate (0.3 g) in anhydrous tetrahydrofuran,cool to -78° C. and place under an argon atmosphere. Add, by dropwiseaddition, n-butyllithium (1.16 mL of a 1.6M solution). Stir for 1/2 hourat -78° C. and add a solution ofN-(9-phenylfluorenyl)-piperidine-2(R)-tert-butyl-3(R)-methyl ester (0.3g, 0.62 mmol) in anhydrous tetrahydrofuran (10 mL). Allow to warm to-30° C. and stir for 3 hours, then cool to -78° C. and quench withacetic acid. Warm to room temperature, pour into ethyl ether (250 mL)and wash with brine (100 mL). Dry (Na₂ SO₄) and evaporate to a residue.Purify by silica gel chromatography (ethyl acetate) to give the titlecompound (0.3 g).

¹ H NMR (300 MHz, CDCl₃) ppm 7.15-7.75 (m, 13), 4.15 (m, 4), 3.79 (m,1), 3.73 (m, 1), 3.05-3.2 (m, 3), 2.72 (m, 1), 1.75-2.05 (m, 3), 1.55(m, 1), 1.35 (m, 7), 1.04 (s, 9).

Step c: 3(R)-(Phosphonoacetyl)piperidine-2(R)-carboxylic acid, methylester

Mix trifluoroacetic acid (30 mL) with acetonitrile (10 mL) and add, bydropwise addition, to an ice-cold solution ofN-(9-phenylfluorenyl)-3-(R)-[(diethoxyphosphinyl)acetyl]piperidine-2(R)-carboxylicacid, tert-butyl ester (3.5 g, 5.8 mmol) in acetonitrile (40 mL) andwater (4 mL). Stir for 15 minutes, warm to room temperature and stir foran additional hour. Pour into saturated aqueous sodium hydrogencarbonate (500 mL) and extract into ethyl acetate (3×200 mL). Evaporateto a residue and take up the residue in acetonitrile (20 mL) andmethylene chloride (20 mL). Place under a nitrogen atmosphere and addtrimethylsilyl chloride (5 mL, 35 mmol). Stir overnight then add water.Stir for 15 minutes then blow to a residue with a stream of drynitrogen. Take up the residue in water (100 mL) and wash with toluene(5×100 mL). Freeze dry to give a residue. Take up the residue inmethanol (10 mL) and isopropanol (5 mL). Add propylene oxide (5 mL) andfilter to give the title compound.

The 2(R),3(S) saturated piperidine compounds of Formula I wherein R₅ isrepresented by linear C₁ -C₄ alkyl, or phenylalkyl can be prepared bytechniques and procedures well known and appreciated by one of ordinaryskill in the art. A general synthetic scheme for preparing thesecompounds is set forth in Scheme H. In Scheme H all substituents unlessotherwise indicated are as previously defined. ##STR24##

Scheme H provides a general synthetic procedure for preparing the2(R),3(S) saturated piperidine compounds of Formula I wherein R₅ isrepresented by linear C₁ -C₄ alkyl, or phenylalkyl.

In step a, the appropriate α-C₁ -C₄ alkyl orbenzyl-β-methyl-N-(3-iodopropyl)-N-(9-phenylfluorenyl)-D-aspartate ofstructure (34) is alkylatively cyclized with the appropriate alkylatingagent of the formula R₅ -Hal, wherein Hal is Br or I, to give thecorresponding N-(9-phenylfluorenyl)piperidine-2(R)-C₁ -C₄ alkyl orbenzyl ester-3(R)-alkyl-3(S)-methyl ester of structure (41). Theappropriate alkylating agent of the formula R₅ -Hal, wherein Hal is Bror I is one in which R₅ is the same as is desired in the final product.

For example, the appropriate α-C₁ -C₄ alkyl orbenzyl-β-methyl-N-(3-iodopropyl)-N-(9-phenylfluorenyl)-D-aspartate ofstructure (34) is contacted with an appropriate base such as lithiumdiisopropylamine. The reactants are typically contacted in a suitableorganic solvent such as tetrahydrofuran. The reactants are typicallystirred together for a period of time ranging from 2-20 hours and at atemperature range of from -78° C. to -20° C. TheN-(9-phenylfluorenyl)-piperidine-2(S)-C₁ -C₄ alkyl or benzylester-3(R)-alkyl-3(S)-methyl ester of structure (41) is recovered fromthe reaction zone by a low-temperature quench into an appropriatealkylating agent of the formula R₅ -Hal, followed by acidification andextraction as is known in the art. It may be purified by silica gelchromatography.

In step b, the appropriate N-(9-phenylfluorenyl)piperidine-2(R)-C₁ -C₄alkyl or benzyl ester-3(R)-alkyl-3(S)-methyl ester of structure (41) iscoupled with the appropriate phosphonate ester of structure (5) to givethe correspondingN-(9-phenylfluorenyl)-3(S)-[(dialkoxyphosphinyl)acetyl]piperidine-3(R)-alkyl-2(R)-carboxylicacid, benzyl or C₁ -C₄ alkyl ester of structure (42) as describedpreviously in Scheme A, step d.

In step c, the appropriateN-(9-phenylfluorenyl)-3(S)-[(dialkoxyphosphinyl)acetyl]piperidine-3(R)-alkyl-2(R)-carboxylicacid, benzyl or C₁ -C₄ alkyl ester of structure (42) is deprotected togive the corresponding3(S)-[(dialkoxyphosphinyl)acetyl]piperidine-3(R)-alkyl-2(R)-carboxylicacid, benzyl or C₁ -C₄ alkyl ester of structure (43).

The appropriate3(S)-[(dialkoxyphosphinyl)acetyl]piperidine-3(R)-alkyl-2(R)-carboxylicacid, benzyl or C₁ -C₄ alkyl ester of structure (43) can be furtherfunctionalized as described previously in Scheme A, steps g₁ -i.

The appropriate 3(S)-[(functionalizedphosphinyl)acetyl]piperidine-3(R)-alkyl-2(R)-carboxylic acid derivativesof Formula I prepared as described above in Scheme H may also be furtherfunctionalized into the corresponding3(S)-[1-imino-2-phosponoethyl]piperidine-3(R)-alkyl-2(R)-carboxylic acidderivatives of Formula I as described previously in Scheme C, step a.

Alternatively, the enantiomerically pure 2(S),3(R) saturated piperidinecompounds of Formula I wherein R₅ is represented by linear C₁ -C₄ alkyl,or phenylalkyl can be prepared as set forth in Scheme H by substitutingthe appropriate N-(9-phenylfluorenyl)piperidine-2(S)-C₁ -C₄ alkyl orbenzyl ester-3(R)-methyl ester for the appropriateN-(9-phenylfluorenyl)piperidine-2(R)-C₁ -C₄ alkyl or benzylester-3(S)-methyl ester of structure (35). The appropriateN-(9-phenylfluorenyl)piperidine-2(S)-C₁ -C₄ alkyl or benzylester-3(R)-methyl ester can be prepared as set forth in Scheme F bysubstituting L-aspartic acid for the D-aspartic acid (28).

Starting materials for use in Scheme H are readily available to one ofordinary skill in the art.

The following examples present typical syntheses as described in SchemeH. These examples are intended to be illustrative only and are notintended to limit the scope of the present invention in any way.

Example 11

3(S)-(Phosphonoacetyl)piperidine-3(R) -methyl-2(R)-carboxylic acid##STR25## Step a:N-(9-Phenylfluorenyl)piperidine-3(R)-methyl-2(R)-tert-butylester-3(S)-methyl ester

Dissolve diisopropylamine (0.73 mL) in anhydrous tetrahydrofuran (10mL), cool to 0° C. and place under an inert atmosphere. Add, by dropwiseaddition, n-butyllithium (3.11 mL of a 1.6M solution in hexane) and stirfor 15 minutes at 0° C. then at -78° C. for 15 minutes. Add, by dropwiseaddition, a solution ofα-tert-butyl-β-methyl-N-(3-iodopropyl)-N-(9-phenylfluorenyl)-D-aspartate(1.22 g) in anhydrous tetrahydrofuran (10 mL). Stir for 1 hour at -78°C. then at -38° C. for 3 hours. Cool to -78° C. and add via cannula to asolution of iodomethane (3 mL) in tetrahydrofuran (10 mL). Stir at -78°C. for 3 hours, quench with acetic acid and warm to room temperature.Evaporate to a residue and purify by silica gel chromatography(methylene chloride) to give impure title compound.

Dissolve diisopropylamine (0.35 mL, 2.5 mmol) in anhydroustetrahydrofuran, cool to 0° C. and place under an inert atmosphere. Add,by dropwise addition, n-butyllithium (1.4 mL of a 1.6M solution inhexane, 2.5 mmol) and stir for 1/2 hour at 0° C. Cool to -78° C. and addhexamethylphosphoramide (0.43 mL, 2.5 mmol) followed by a solution ofN-(9-phenylfluorenyl)piperidine-2(S)-tert-butyl ester-3(S)-methyl ester(0.8 g, 1.7 mmol) in anhydrous tetrahydrofuran (5 mL). Stir for 1/2 hourand add iodomethane (0.42 mL, 6.8 mmol). Stir at -78° C. overnight,quench with acetic acid and warm to room temperature. Evaporate to aresidue and purify by silica gel chromatography (80:20/methylenechloride/hexane) to give the title compound (0.56 g).

¹ H NMR (300 MHz, CDCl₃) ppm 7.18-7.75 (m, 13), 3.93 (s, 1), 3.88 (s,3), 3.82 (m, 1), 3.08 (m, 1), 2.59 (m, 1), 2.14 (m, 1), 1.98 (m, 1),1.78 (m, 1), 1.62 (m, 1), 1.08 (s, 9).

Step b:N-(9-Phenylfluorenyl)-3(S)-[(diethoxyphosphinyl)acetyl]piperidine-3(R)-methyl-2(R)-carboxylicacid, tert-butyl ester

Dissolve diethyl methylphosponate (1.14 g, 7.5 mmol) in anhydroustetrahydrofuran (10 mL), cool to -78° C. and place under an inertatmosphere. Add n-butyllithium (4.68 mL of a 1.6M solution in hexane,7.5 mmol) and stir for 20 minutes. Add, by dropwise addition, a solutionof N-(9-phenylfluorenyl)piperidine-3(R)-methyl-2(R)-tert-butylester-3(S)-methyl ester (0.55 g, 1.1 mmol) in anhydrous tetrahydrofuran(10 mL). Stir for 4 hours at -48° C. and add acetic acid (2 mL). Warm toroom temperature, evaporate to a residue and purify by silica gelchromatography (ethyl acetate) to give the title compound (0.33 g).

¹ H.NMR (300 MHz, CDCl₃)ppm 7.18-8.75 (m, 13), 4.10 (m, 4), 3.54 (m, 1),3.51 (s, l), 3.15 (m, 1), 2.99 (m, 2), 2.48 (m, 1), 1.98 (m, 1), 1.29(m, 6), 0.92 (s, 9).

Step c: 3(S)-(Phosphonoacetyl)piperidine-3(R)-methyl-2(R)-carboxylicacid

Dissolve N-(9-phenylfluorenyl)-3(S)-[(diethoxyphosphinyl)acetyl]piperidine-3(R)-methyl-2(R)-carboxylicacid, tert-butyl ester (0.35 g) in acetonitrile and cool to 0° C. Stirvigorously and add, by dropwise addition, a solution of trifluoroaceticacid (20 mL) in water (2 mL). Stir for 15 minutes, warm to roomtemperature and stir for 3 hours. Evaporate the a solid residue, take upin water (100 mL) and wash with toluene (100 mL). Freeze dry the aqueousphase to give a white solid. Take up the white solid in acetonitrile (10mL) and methylene chloride (10 mL). Pass a gentle stream of nitrogenthrough the solution and add trimethylsilyliodide (2 mL). Stir for 6hours, quench with water and wash with toluene (5×100 mL). Freeze drythe aqueous phase and dissolve the resulting yellow solid in methanol (5mL) and isopropanol (2.5 mL). Add propylene oxide (2.0 mL) and stir for2 hours. Filter to give the title compound.

¹ H NMR (300 MHz, D₂ O) ppm, 3.69 (s, 1), 3.32 (m, 1), 2.9 (m, 1), 2.28(m, 1), 1.4-1.8 (m, 3), 1.53 (s, 3).

The following compounds can be prepared in a similar fashion to thatdescribed above in Example 11:

3(S)-(Phosphonoacetyl]piperidine-5-benzyl-3(R)-methyl-2(R)-carboxylicacid.

The 2(R)-3-unsaturated piperidine compounds of Formula I can be preparedby techniques and procedures well known and appreciated by one ofordinary skill in the art. A general synthetic procedure for preparingthese compounds is set forth in Scheme I. In Scheme I all substituentsunless otherwise indicated are as previously defined. ##STR26##

Scheme I provides a general synthetic procedure for preparing the2(R)-3-unsaturated piperidine compounds of Formula I.

In step a, the appropriate α-C₁ -C₄ alkyl orbenzyl-β-methyl-N-(3-iodopropyl)-N-(9-phenylfluorenyl)-D-aspartate ofstructure (34) is cyclized and either iodinated or selenated to give thecorresponding N-(9-phenylfluorenyl)piperidine-3(R)-iodo-2(R)-C₁ -C₄alkyl or benzyl ester-3(S)-methyl ester of structure (44) orN-(9-phenylfluorenyl)piperidine-3-(R)-phenylselenyl-2(R)-C₁ -C₄ alkyl orbenzyl ester-3(S)-methyl ester of structure (44).

For example, the appropriate α-C₁ -C₄ alkyl orbenzyl-β-methyl-N-(3-iodopropyl)-N-(9-phenylfluorenyl)-D-aspartate ofstructure (34) is contacted with an appropriate base such as lithiumdiisopropylamine. The reactants are typically contacted in a suitableorganic solvent such as tetrahydrofuran. The reactants are typicallystirred together for a period of time ranging from 2-20 hours and at atemperature range of from -78° C. to -20° C. TheN-(9-phenylfluorenyl)piperidine-3(R)-iodo-2(R)-C₁ -C₄ alkyl or benzylester-3(S)-methyl ester of structure (44) orN-(9-phenylfluorenyl)piperidine-3(R)-phenylselenyl-2(R)-C₁ -C₄ alkyl orbenzyl ester-3(S)-methyl ester of structure-(44) is recovered from thereaction zone by a low-temperature quench into iodine ordiphenyldiselenide, followed by acidification and extraction as is knownin the art. It may be purified by silica gel chromatography.

When N-(9-phenylfluorenyl)piperidine-3(R)-phenylselenyl-2(R)-C₁ -C₄alkyl or benzyl ester-3(S)-methyl ester of structure (44) is prepared instep a, the selenyl functionality must be subsequently oxidized bytechniques well known in the art to give the correspondingN-(9-phenylfluorenyl)piperidine-3(R)-phenylselenoxyl-2(R)-C₁ -C₄ alkylor benzyl ester-3(S)-methyl ester before continuing with step b.

In step b, the appropriateN-(9-phenylfluorenyl)piperidine-3(R)-iodo-2(R)-C₁ -C₄ alkyl or benzylester-3(S)-methyl ester of structure (44) orN-(9-phenylfluorenyl)piperidine-3(R)-phenylselenoxyl-2(R)-C₁ -C₄ alkylor benzyl ester-3(S)-methyl ester is eliminated to give thecorresponding N-(9-phenylfluorenyl)-3-piperidene-2(R)-C₁ -C₄ alkyl orbenzyl ester-3-methyl ester of structure (45).

For example, the appropriateN-(9-phenylfluorenyl)piperidine-3(R)-iodo-2(R)-C₁ -C₄ alkyl or benzylester-3(S)-methyl ester of structure (44) orN-(9-phenylfluorenyl)piperidine-3(R)-phenylselenoxyl-2(R)-C₁ -C₄ alkylor benzyl ester-3(S)-methyl ester is contacted with a molar excess of astrong base, such as 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). Thereactants are typically contacted in a suitable organic solvent such asbenzene. The reactants are typically stirred together for a period oftime ranging from 2-24 hours and at a temperature range of from roomtemperature to 80° C. The N-(9-phenylfluorenyl)-3-piperidene-2(R)-C₁ -C₄alkyl or benzyl ester-3-methyl ester of structure (45) is recovered fromthe reaction zone by extractive methods as is known in the art. It maybe purified by silica gel chromatography.

In step c, the appropriate N-(9-phenylfluorenyl)-3-piperidene-2(R)-C₁-C₄ alkyl or benzyl ester-3-methyl ester of structure (45) is coupledwith the appropriate phosphonate ester of structure (5) to give thecorrespondingN-(9-phenylfluorenyl)-3-[(dialkoxyphosphinyl)acetyl]-3-piperidene-2(R)-carboxylicacid, benzyl or C₁ -C₄ alkyl ester of structure (46) as describedpreviously in Scheme A, step d.

In step d, the appropriateN-(9-phenylfluorenyl)-3-[(dialkoxyphosphinyl)acetyl]-3-piperidene-2(R)-carboxylicacid, benzyl or C₁ -C₄ alkyl ester of structure (46) is deprotected togive the corresponding3-[(dialkoxyphosphinyl)acetyl]-3-piperidene-2(R)-carboxylic acid, benzylor C₁ -C₄ alkyl ester of structure (47) as described previously inScheme A, step f.

The appropriate3-[(dialkoxyphosphinyl)acetyl]-3-piperidene-2(R)-carboxylic acid, benzylor C₁ -C₄ alkyl ester of structure (47) can be further functionalized asdescribed previously in Scheme A, steps g₁ -i.

The appropriate 3-[(functionalizedphosphinyl)acetyl]-3-piperidene-2(R)-carboxylic acid derivatives ofFormula I prepared as described above in Scheme H may also be furtherfunctionalized into the corresponding3-[1-imino-2-phosponoethyl]-3-piperidene-2(R)-carboxylic acidderivatives of Formula I as described previously in Scheme C, step a.

Alternatively, the enantiomerically pure 2(S)-3-unsaturated piperidinecompounds of Formula I can be prepared as set forth in Scheme I bysubstituting the appropriate α-C₁ -C₄ alkyl orbenzyl-β-methyl-N-(3-iodopropyl)-N-(9-phenylfluorenyl)-L-aspartate forthe appropriate α-C₁ -C₄ alkyl orbenzyl-β-methyl-N-(3-iodopropyl)-N-(9-phenylfluorenyl)-D-aspartate ofstructure (34). The appropriate α-C₁ -C₄ alkyl orbenzyl-β-methyl-N-(3-iodopropyl)-N-(9-phenylfluorenyl)-L-aspartate canbe prepared as set forth in Scheme F by substituting L-aspartic acid forthe D-aspartic acid (28).

Starting materials for use in Scheme I are readily available to one ofordinary skill in the art.

The following examples present typical syntheses as described in SchemeI. These examples are intended to be illustrative only and are notintended to limit the scope of the present invention in any way.

Example 12

3-(Phosphonoacetyl)-3-piperidene-2 (R) -carboxylic acid ##STR27## Stepa: N-(9-Phenylfluorenyl)piperidine-3(R)-iodo-2(R)-tert-butylester-3(S)-methyl ester

Dissolve diisopropylamine (2.4 mL, 17.12 mmol) in anhydroustetrahydrofuran (80 mL), cool to 0°-5° C. and place under an inertatmosphere. Add n-butyllithium (10.5 mL of a 1.6M solution in hexane,16.8 mmol) and cool to "70°-75° C. Add a solution ofα-tert-butyl-β-methyl-N-(3-iodopropyl)-N-(9-phenylfluorenyl)-D-aspartate(4.0 g, 6.54 mmol) in tetrahydrofuran (10 mL). Stir at -78° C. for 1hour, then warm to -35° C. and stir for 3-4 hours to give the enolate.

Dissolve iodine (2.5 g, 9.85 mmol) in tetrahydrofuran (30 mL) and coolto -78° C. Add the -40° C. solution of the enolate and stir overnight,slowly warming to room temperature. Add phosphoric acid (20 mL of a 0.5Msolution) and extract into ethyl ether (3×20 mL). Combine the organicphases and wash with saturated sodium thiosulfate (10 mL) and saturatedsodium hydrogen carbonate (20 mL). Dry (MgSO₄ /Na₂ SO₄) and evaporatethe solvent in vacuo to give the title compound (3.99 g).

¹ H NMR (300 MHz, CDCl₃) ppm 7.1-1.9 (m, 13), 4.01 (s, 1), 3.75 (m, 1),3.65 (s, 3), 3.28 (m, 1), 3.18 (m, 1), 2.2-2.4 (m, 1), 1.8 (m, 1), 1.3(m, 1), 0.9 (s, 9).

Step b: N-(9-Phenylfluorenyl)-3-piperidene-2(R)-tert-butylester-3-methyl ester

Mix N-(9-phenylfluorenyl)piperidine-3(R)-iodo-2(R)-tert-butylester-3(S)-methyl ester (3.99 g, 6.55 mmol),1,8-diazabicyclo[5.4.0]undec-7-ene (2.9 mL, 19.62 mmol) and benzene (8.5mL). Heat to 65° C. of several hours. Add phosphoric acid (50 mL of a0.5M solution) and extract into ethyl ether (4×20 mL). Dry (MgSO₄ /Na₂SO₄), evaporate the solvent in vacuo and purify by silica gelchromatography (30/70 ethyl ether/hexane) to give the title compound.

¹ H NMR (300 MHz, CDCl₃ ) ppm 7.15-7.75 (m, 13), 6.98 (m, 1), 4.51 (s,1), 3.68 (s, 3), 3.38 (m, 1), 3.05 (m, 1), 1.89 (m, 2), 1.2 (s, 9).

Step c:N-(9-phenylfluorenyl)-3-[(diethoxyphosphinyl)acetyl]-3-piperidene-2(R)-carboxylicacid, tert-butyl ester

Dissolve diethyl methylphosponate (1.14 g, 7.5 mmol) in anhydroustetrahydrofuran (10 mL), cool to -78° C. and place under an inertatmosphere. Add n-butyllithium (4.68 mL of a 1.6M solution in hexane,7.5 mmol) and stir for 20 minutes. Add, by dropwise addition, a solutionof N-(9-phenylfluorenyl-3-piperidene-2(R)-tert-butyl ester-3-methylester (545 mg, 1.1 lmmol) in anhydrous tetrahydrofuran (10 mL). Stir for4 hours at -48° C. and add acetic acid (2 mL). Warm to room temperature,evaporate to a residue and purify by silica gel chromatography (ethylacetate) to give the title compound.

Step d: 3-(Phosphonoacetyl)-3-piperidene-2(R)-carboxylic acid DissolveN-(9-phenylfluorenyl)-3-[(diethoxyphosphinyl)acetyl]-3-piperidene-2(R)-carboxylicacid, tert-butyl ester (0.35 g) in acetonitrile and cool to 0° C. Stirvigorously and add, by dropwise addition, a solution of trifluoroaceticacid (20 mL) in water (2 mL). Stir for 15 minutes, warm to roomtemperature and stir for 3 hours. Evaporate the a solid residue, take upin water (100 mL) and wash with toluene (100 mL). Freeze dry the aqueousphase to give a residue. Take up the residue in acetonitrile (10 mL) andmethylene chloride (10 mL). Pass a gentle stream of nitrogen through thesolution and add trimethylsilyliodide (2 mL). Stir for 6 hours, quenchwith water and wash with toluene (5×100 mL). Freeze dry the aqueousphase and dissolve the resulting residue in methanol (5 mL) andisopropanol (2.5 mL). Add propylene oxide (2.0 mL) and stir for 2 hours.Filter to give the title compound.

The following compound can be prepared in a similar fashion to thatdescribed above in Example 12:

3-(Phosphonoacetyl)-3-piperidene-5-methyl-2(R)-carboxylic acid.

The 2(R),3(S)-4-unsaturated piperidine compounds of Formula I can beprepared by techniques and procedures well known and appreciated by oneof ordinary skill in the art. A general synthetic procedure forpreparing these compounds is set forth in Scheme J. In Scheme J allsubstituents unless otherwise indicated are as previously defined.##STR28##

Scheme J provides a general synthetic scheme for preparing the2(S),3(S)-4-unsaturated piperidine compounds of Formula I.

In step a, the appropriate N-(9-phenylfluorenyl)-3-piperidene-2(R)-C₁-C₄ alkyl or benzyl ester-3-methyl ester of structure (45) undergoes adeconjucative alkylation to give the correspondingN-(9-phenylfluorenyl)-4-piperidene-2(R)-C₁ -C₄ alkyl or benzylester-3-methyl ester of structure (48).

For example, the appropriate N-(9-phenylfluorenyl)-3-piperidene-2(R)-C₁-C₄ alkyl or benzyl ester-3-methyl ester of structure (45) is contactedwith a strong base, such as n-butyllithium. The reactants are typicallycontacted in a suitable organic solvent such as tetrahydrofuran. Thereactants are typically stirred together for a period of time rangingfrom 1-10 hours and at a temperature range of from -78° C. to -20° C.The N-(9-phenylfluorenyl)-4-piperidene-2(R)-C₁ -C₄ alkyl or benzylester-3-methyl ester of structure (48) is recovered from the reactionzone by a low-temperature quench into an appropriate alkylating agent ofthe formula R₅ -Hal or a proton source such as diisopropyl phenol,followed by acidification and extraction as is known in the art. It maybe purified by silica gel chromatography.

In step b, the appropriate N-(9-phenylfluorenyl)-4-piperidene-2(R)-C₁-C₄ alkyl or benzyl ester-3-methyl ester of structure (48) is coupledwith the appropriate phosphonate ester of structure (5) to give thecorrespondingN-(9-phenylfluorenyl)-3(S)-[(dialkoxyphosphinyl)acetyl]-4-piperidene-2(R)-carboxylicacid, benzyl or C₁ -C₄ alkyl ester of structure (49) as describedpreviously in Scheme A, step d.

In step c, the appropriateN-(9-phenylfluorenyl)-3(S)-[(dialkoxyphosphinyl)acetyl]-4-piperidene-2(R)-carboxylicacid, benzyl or C₁ -C₄ alkyl ester of structure (49) is deprotected togive the corresponding3(S)-[(dialkoxyphosphinyl)acetyl]-4-piperidene-2(R)-carboxylic acid,benzyl or C₁ -C₄ alkyl ester of structure (50) as described previouslyin Scheme A, step f.

The appropriate3(S)-[(dialkoxyphosphinyl)acetyl]-4-piperidene-2(R)-carboxylic acid,benzyl or C₁ -C₄ alkyl ester of structure (50) can be furtherfunctionalized as described previously in Scheme A, steps g₁ -i.

The appropriate 3(S)-[(functionalizedphosphinyl)acetyl]-4-piperidene-2(R)-carboxylic acid derivatives ofFormula I prepared as described above in Scheme J may also be furtherfunctionalized into the corresponding3(S)-[1-imino-2-phosponoethyl]-4-piperidene-2(R)-carboxylic acidderivatives of Formula I as described previously in Scheme C, step a.

Alternatively, the enantiomerically pure the 2(S),3(R)-4-unsaturatedpiperidine compounds of Formula I can be prepared as set forth in SchemeI by substituting the appropriateN-(9-phenylfluorenyl)-3-piperidene-2(S)-C₁ -C₄ alkyl or benzylester-3-methyl ester for the appropriateN-(9-phenylfluorenyl)-3-piperidene-2(R)-C₁ -C₄ alkyl or benzylester-3-methyl ester of structure (45). The appropriateN-(9-phenylfluorenyl)-3-piperidene-2(S)-C₁ -C₄ alkyl or benzylester-3-methyl ester can be prepared as set forth in Scheme I bysubstituting the appropriate α-C₁ -C₄ alkyl orbenzyl-β-methyl-N-(3-iodopropyl)-N-(9-phenylfluorenyl)-L-aspartate forthe appropriate α-C₁ -C₄ alkyl orbenzyl-β-methyl-N-(3-iodopropyl)-N-(9-phenylfluorenyl)-L-aspartate ofstructure (34). The appropriate α-C₁ -C₄ alkyl orbenzyl-β-methyl-N-(3-iodopropyl)-N-(9-phenylfluorenyl)-L-aspartate canbe prepared as set forth in Scheme F by substituting L-aspartic acid forthe D-aspartic acid (28).

In addition, the enantiomerically pure 2(R),3(R)-4-unsaturatedpiperidine compounds of Formula I can be prepared as set forth in SchemeI by substituting the appropriateN-(benzyloxycarbonyl)-3-piperidene-2(R)-C₁ -C₄ alkyl or benzylester-3-methyl ester for the appropriateN-(9-phenylfluorenyl)-3-piperidene-2(R)-C₁ -C₄ alkyl or benzylester-3-methyl ester of structure (45) followed by an HPLC separation asset forth in Scheme B.

Alternatively, the enantiomerically pure 2(S),3(S)-4-unsaturatedpiperidine compounds of Formula I can be prepared as set forth in SchemeI by substituting the appropriateN-(benzyloxycarbonyl)-3-piperidene-2(S)-C₁ -C₄ alkyl or benzylester-3-methyl ester for the appropriateN-(9-phenylfluorenyl)-3-piperidene-2(S)-C₁ -C₄ alkyl or benzylester-3-methyl ester of structure (45) followed by an HPLC separation asset forth in Scheme B. The appropriateN-(benzyloxycarbonyl)-3-piperidene-2(S)-C₁ -C₄ alkyl or benzylester-3-methyl ester can be prepared as set forth in Scheme I bysubstituting the appropriate α-C₁ -C₄ alkyl orbenzyl-β-methyl-N-(3-iodopropyl)-N-(9-phenylfluorenyl)-L-aspartate forthe appropriate α-C₁ -C₄ alkyl orbenzyl-β-methyl-N-(3-iodopropyl)-N-(9-phenylfluorenyl)-L-aspartate ofstructure (34). The appropriate α-C₁ -C₄ alkyl orbenzyl-β-methyl-N-(3-iodopropyl)-N-(9-phenylfluorenyl)-L-aspartate canbe prepared as set forth in Scheme F by substituting L-aspartic acid forthe D-aspartic acid (28).

Starting materials for use in Scheme J are readily available to one ofordinary skill in the art.

The following examples present typical syntheses as described in SchemeJ. These examples are intended to be illustrative only and are notintended to limit the scope of the present invention in any way.

Example 13

3(S)-(Phosphonoacetyl)-4-piperidene-2(R)-carboxylic acid ##STR29## Stepa: N-(9-Phenylfluorenyl)-4-piperidene-2(R)-carboxylic acid tert-butylester

Dissolve diisopropylamine (12 mL, 85.6 mmol) in anhydroustetrahydrofuran, cool to -78° C. and place under an inert atmosphere.Add n-butyllithium (52 mL of a 1.6M solution in hexane, 83.2 mmol) andstir at -78° C. for 20 minutes. Add hexamethylphosphoramide and add, bydropwise addition, a solution ofN-(9-phenylfluorenyl)-3-piperidene-2(R)-tert-butyl ester-3-methyl ester(16.2 g, 32.7 mmol) in anhydrous tetrahydrofuran (50 mL). Stir at -78°C. for 1 hour, warm to -48° C. and stir for 3 hours. Cool to -78° C. andtransfer via cannula to a -78° C. solution of diisopropyl phenol (30.8g, 0.17 mol) in tetrahydrofuran (200 mL). Stir for 1 hour and add addacetic acid (5.2 mL). Warm to room temperature and quench with water(100 mL). Partition between methylene chloride (500 mL) and water (300mL). Separate the organic phase, dry (Na₂ SO₄) and evaporate to aresidue. Purify by silica gel chromatography to give the title compound.

Step b:N-(9-Phenylfluorenyl)-3(S)-[(diethoxyphosphinyl)acetyl]-4-piperidene-2(R)-carboxylicacid, tert-butyl ester

Dissolve diethyl methylphosponate (1.14 g, 7.5 mmol) in anhydroustetrahydrofuran (10 mL), cool to -78° C. and place under an inertatmosphere. Add n-butyllithium (4.68 mL of a 1.6M solution in hexane,7.5 mmol) and stir for 20 minutes. Add, by dropwise addition, a solutionof N-(9-phenylfluorenyl)-4-piperidene-2(R)-carboxylic acid, tert-butylester (529 mg, 1.1 mmol) in anhydrous tetrahydrofuran (10 mL). Stir for4 hours at -48° C. and add acetic acid (2 mL). Warm to room temperature,evaporate to a residue and purify by silica gel chromatography (ethylacetate) to give the title compound.

Step c: 3(S)-(Phosphonoacetyl)-4-piperidene-2(R)-carboxylic acid

DissolveN-(9-phenylfluorenyl)-3(S)-[(diethoxyphosphinyl)acetyl]-4-piperidene-2(R)-carboxylicacid, tert-butyl ester (0.35 g) in acetonitrile and cool to 0° C. Stirvigorously and add, by dropwise addition, a solution of trifluoroaceticacid (20 mL) in water (2 mL). Stir for 15 minutes, warm to roomtemperature and stir for 3 hours. Evaporate to a solid residue, take upin water (100 mL) and wash with toluene (100 mL). Freeze dry the aqueousphase to give a residue. Take up the residue in acetonitrile (10 mL) andmethylene chloride (10 mL). Pass a gentle stream of nitrogen through thesolution and add trimethylsilyliodide (2 mL). Stir for 6 hours, quenchwith water and wash with toluene (5×100 mL). Freeze dry the aqueousphase and dissolve the resulting residue in methanol (5 mL) andisopropanol (2.5 mL). Add propylene oxide (2.0 mL) and stir for 2 hours.Filter to give the title compound.

Example 14

3(S)-(Phosphonoacetyl)-3-(R)-methyl-4-piperidene-2(R) -carboxylic acid##STR30## Step a:N-(9-Phenylfluorenyl)-3(R)-methyl-4-piperidene-2(R)-carboxylic acid,tert-butyl ester

Dissolve diisopropylamine (0.17 mL, 0.79 mmol) in anhydroustetrahydrofuran (4.8 mL), cool to 0° C. and place under an inertatmosphere. Add n-butyllithium (0.75 mL of a 1.6M solution in hexane,1.20 mmol) and cool to -78° C. Add, by dropwise addition,hexamethylphosphoramide (0.22 mL. 1.26 mmol), keeping the temperaturebelow -60° C. Stir at -78° C. for 30 minutes and add, by dropwiseaddition, a solution ofN-(9-phenylfluorenyl)-3-piperidene-2(R)-tert-butyl ester-3-methyl ester(380mg, 0.79 mmol) in anhydrous tetrahydrofuran (5 mL). Warm to -50° C.to -45° C. and stir for 1 hour, maintaining a temperature of -50° C. to-38° C. Cool to -78° C. and transfer via cannula to a -78° C. solutionof iodomethane (0.21 mL, 3.37 mmol). Stir at - 78° C. overnight and addadd methanol (2 mL) and phosphoric acid (15 mL of a 0.5M solution).Extract into ether ether (3×mL), dry (Na₂ SO₄ /MgSO₄) and evaporate thesolvent in vacuo to give a dark yellow oil. Purify by silica gelchromatography (25/75 ethyl acetate/hexane) to give the title compound(170 mg, 43%).

¹ H NMR (300 MHz, CDCl₃) ppm 7.15-7.8 (m, 13), 6.12 (m, 1), 5.80 (m, 1),3.84 (m, 1), 3.68 (s, 1), 3.52 (s, 3), 2.69 (s, 3), 1.25 (m, 1), 0.92(s, 9).

Sep b:N-(9-Phenylfluorenyl),3(S)-[(diethoxyphosphinyl)acetyl]-3-(R)-methyl-4-piperidene-2(R)-carboxylicacid, tert-butyl ester

Dissolve diethyl methylphosponate (1.14 g, 7.5 mmol) in anhydroustetrahydrofuran (10 mL), cool to -78° C. and place under an inertatmosphere. Add n-butyllithium (4.68 mL of a 1.6M solution in hexane,7.5 mmol) and stir for 20 minutes. Add, by dropwise addition, a solutionof N-(9-Phenylfluorenyl)-3(R)-methyl-4-piperidene-2(R)-carboxylic acid,tert-butyl ester (560mg, 1.1 mmol) in anhydrous tetrahydrofuran (10 mL).Stir for 4 hours at -48° C. and add acetic acid (2 mL). Warm to roomtemperature, evaporate to a residue and purify by silica gelchromatography (ethyl acetate) to give the title compound.

Step c: 3(S)-(Phosphonoacetyl)-3(R)-methyl-4-piperidene-2(R)-carboxylicacid

DissolveN-(9-phenylfluorenyl)-3(S)-[(diethoxyphosphinyl)acetyl]-3(R)-methyl-4-piperidene-2(R)-carboxylicacid, tert-butyl ester (0.35 g) in acetonitrile and cool to 0° C. Stirvigorously and add, by dropwise addition, a solution of trifluoroaceticacid (20 mL) in water (2 mL). Stir for 15 minutes, warm to roomtemperature and stir for 3 hours. Evaporate to a solid residue, take upin water (100 mL) and wash with toluene (100 mL). Freeze dry the aqueousphase to give a residue. Take up the residue in acetonitrile (10 mL) andmethylene chloride (10 mL). Pass a gentle stream of nitrogen through thesolution and add trimethylsilyliodide (2 mL). Stir for 6 hours, quenchwith water and wash with toluene (5×100 mL). Freeze dry the aqueousphase and dissolve the resulting residue in methanol (5 mL) andisopropanol (2.5 mL). Add propylene oxide (2.0 mL) and stir for 2 hours.Filter to give the title compound.

The following compounds can be prepared in a similar fashion to thatdescribed above in Examples 13 and 14:

3(S)-(Phosphonoacetyl)-3(R)-methyl-5-methyl-4-piperidene-2(R)-carboxylicacid;

3(S)-(Phosphonoacetyl)-3(R)-methyl-5-benzyl-4-piperidene-2(R)-carboxylic acid.

The pyrrolidine compounds of Formula I wherein R₅ is hydrogen can beprepared by techniques and procedures well known and appreciated by oneof ordinary skill in the art. A general synthetic procedure forpreparing these compounds is set forth in Scheme K. In Scheme K allsubstituents unless otherwise indicated are as previously defined.##STR31##

Scheme K provides a general synthetic procedure for preparing thepyrrolidine compounds of Formula I wherein R₅ is hydrogen.

In step a, the 4-chloro functionality of the appropriate ethyl4-chlorobutyrate of structure (51) is exchanged to give thecorresponding ethyl 3-iodobutyrate of structure (52) as describedpreviously in Scheme F, step e.

In step b, the 4-iodo functionality of the appropriate ethyl4-iodobutyrate of structure (52) is displaced with dibenzylamine to givethe corresponding 4-dibenzylaminobutyric acid, ethyl ester of structure(53).

For example, the appropriate ethyl 4-iodobutyrate of structure (52) iscontacted with a molar equivalent of benzylamine and a molar equivalentof a suitable base, such as potassium carbonate. The reactants aretypically contacted in a suitable organic solvent such as ethanol. Thereactants are typically stirred together at room temperature for aperiod of time ranging from 2-24 hours. The 4-dibenzylaminobutyric acid,ethyl ester of structure (53) is recovered from the reaction zone byevaporation of the solvent. It may be purified by silica gelchromatography.

In step c, the appropriate 4-dibenzylaminobutyric acid, ethyl ester ofstructure (53) is alkylated with an appropriate dialkyl oxylate ofstructure (54) to give the corresponding4-dibenzylamino-2-alkyloxylyl-butyric acid, ethyl ester of structure(55).

For example, the appropriate 4-dibenzylaminobutyric acid, ethyl ester ofstructure (53) is contacted with a molar equivalent of the appropriatedialkyl oxylate of structure (54) and a molar equivalent of a base suchas potassium carbonate. The reactants are typically contacted in asuitable organic solvent mixture such as ethanol/benzene. The reactantsare typically stirred together at a temperature range of from roomtemperature to reflux for a period of time of from 2-24 hours. The4-dibenzylamino-2-alkyloxylyl-butyric acid, ethyl ester of structure(55) is recovered from the reaction zone by acidification andevaporation of the solvent. It may be purified by silica gelchromatography.

In step d, the appropriate 4-dibenzylamino-2-alkyloxylyl-butyric acid,ethyl ester of structure (55) is cyclyzed to give the correspondingd,l-cis-pyrrolidine-2-alkylcarboxylate-3-ethylcarboxylate of structure(56).

For example, the appropriate 4-dibenzylamino-2-alkyloxylyl-butyric acid,ethyl ester of structure (55) is contacted with a catalytic amount of ahydrogenation catyalyst such as palladium hydroxide. The reactants aretypically contacted in a suitable organic solvent such as ethanol. Thereactants are typically shaken at room temperature in the presence ofhydrogen at a pressure of 30-50 psi for a period of time ranging from2-16 hours. Thed,l-cis-pyrrolidine-2-alkylcarboxylate-3-ethylcarboxylate of structure(56) is recovered from the reaction zone by filtration and evaporationof the solvent. It may be purified by silica gel chromatography.

In step e, the appropriated,l-cis-pyrrolidine-2-alkylcarboxylate-3-ethylcarboxylate of structure(56) is protected to give the correspondingd,l-cis-N-(9-phenylfluorenyl)pyrrolidine-2-alkylcarboxylate-3-ethylcarboxylateof structure (57) as described previously in Scheme A, step b.

In step f, the appropriated,l-cis-N-(9-phenylfluorenyl)pyrrolidine-2-alkylcarboxylate-3-ethylcarboxylateof structure (57) is coupled with the appropriate phosphonate ester ofstructure (5) to give the correspondingd,l-cis-N-(9-phenylfluorenyl)-3-[(dialkoxyphosphinyl)acetyl]pyrrolidine-2-carboxylicacid, ester of structure (58) as described previously in Scheme A, stepd.

In step g, the appropriated,l-cis-N-(9-phenylfluorenyl)-3-[(dialkoxyphosphinyl)acetyl]pyrrolidine-2-carboxylicacid, ester of structure (58) is deprotected to give the correspondingd,l-cis-3-[(dialkoxyphosphinyl)acetyl]pyrrolidine-2-carboxylic acid,ester of structure (59a) and thed,l-trans-3-[(dialkoxyphosphinyl)acetyl]pyrrolidine-2-carboxylic acid,ester of structure (59b) as described previously in Scheme A, step f.

The appropriated,l-cis-3-[(dialkoxyphosphinyl)acetyl]pyrrolidine-2-carboxylic acid,ester of structure (59a) and thed,l-trans-3-[(dialkoxyphosphinyl)acetyl]pyrrolidine-2-carboxylic acid,ester of structure (59b) can be separated into their diastereomericpairs as shown previously in Scheme B.

Alternatively the enantiomericaly pure3(S)-(dialkoxyphosphinyl)acetyl]pyrrolidine-2(R)-carboxylic acid, esterand enantiomericaly pure3(R)-[(dialkoxyphosphinyl)acetyl]pyrrolidine-2(S)-carboxylic acid, estercan be prepared as set forth in Scheme K by subjecting the appropriated,l-cis-3-[(dialkoxyphosphinyl)acetyl]pyrrolidine-2-carboxylic acid,ester of structure (59a) and thed,l-trans-3-[(dialkoxyphosphinyl)acetyl]pyrrolidine-2-carboxylic acid,ester of structure (59b) to an enzymatic hydrolysis as describedpreviously in Scheme D, step c and Scheme E, optional step d.

In addition, the enantiomericaly pure3(S)-[(dialkoxyphosphinyl)acetyl]pyrrolidine-2(R)-carboxylic acid, esterand enantiomericaly pure3(R)-[(dialkoxyphosphinyl)acetyl]pyrrolidine-2(S)-carboxylic acid, estercan be prepared as set forth in Scheme K by subjecting the appropriated,l-cis-3-[(dialkoxyphosphinyl)acetyl]pyrrolidine-2-carboxylic acid,ester of structure (59a) to an enzymatic hydrolysis as describedpreviously in Scheme D, step c and Scheme E, optional step d.

Similarly, the enantiomericaly pure3(S)-[(dialkoxyphosphinyl)acetyl]pyrrolidine-2(S)-carboxylic acid, esterand enantiomericaly pure3(R)-[(dialkoxyphosphinyl)acetyl]pyrrolidine-2(R)-carboxylic acid, estercan be prepared as set forth in Scheme K by subjecting the appropriated,l-trans-3-[(dialkoxyphosphinyl)acetyl]pyrrolidine-2-carboxylic acid,ester of structure (59b) to an enzymatic hydrolysis as describedpreviously in Scheme D, step c and Scheme E, optional step d.

The appropriate 3-[(dialkoxyphosphinyl)acetyl]pyrrolidine-2-carboxylicacid, ester of Formula I described above in Scheme K can be furtherfunctionalized as described previously in Scheme A, steps g₁ -i.

The appropriate 3-[(functionalizedphosphinyl)acetyl]pyrrolidine-2-carboxylic acid derivatives of Formula Iprepared as described above in Scheme K may also be furtherfunctionalized into the corresponding3-[1-imino-2-phosponoethyl]pyrrolidine-2-carboxylic acid derivatives ofFormula I as described previously in Scheme C, step a.

Starting materials for use in Scheme K are readily available to one ofordinary skill in the art.

The following examples present typical syntheses as described in SchemeK. These examples are intended to be illustrative only and are notintended to limit the scope of the present invention in any way.

Example 15

d,l-cis-3-(Phosphonoacetyl)pyrrolidine-4-methyl-2-carboxylic acid andd,l-trans-3-(Phosphonoacetyl)pyrrolidine-4-methyl-2-carboxylic acid##STR32## Step a: Ethyl 4-iodo-3-methylbutyrate

Mix ethyl 4-chloro-3-methylbutyrate (80 g), acetone (400 mL) and sodiumiodide (100 g). Reflux for 8 hours, cool and add methylene chloride (400mL). Filter and evaporate the filtrate to a residue. Partition theresidue between methylene chloride (200 mL) and water (200 mL). Separatethe organic phase, dry (MgSO₄) and evaporate to an oil. Purify bydistillation to give the title compound.

Step b: 4-Dibenzylamino-3-methylbutyric acid, ethyl ester

Mix ethyl 4-iodo-3-methylbutyrate (4.61 g, 0.18 mol), dibenzylamine(35.5 g, 0.18 mol), potassium carbonate (24.9 g, 0.18 mol) and ethanol(114 mL dried over 4A molecular sieves). Reflux for 24 hours then stirat room temperature for 48 hours. Add methylene chloride (100 mL) andfilter. Evaporate the filtrate to a residue and purify by silica gelchromatography to give the title compound.

Step c: 4-Dibenzylamino-3-methyl-2-tert-butyloxylyl-butyric acid, ethylester

Mix 4-dibenzylamino-3-methylbutyric acid, ethyl ester (20.5 g, 63 mmol), tert-butyl methyl oxylate (10 g, 63 mmol), potassium carbonate (9.3g), ethanol (5 mL) and benzene (150 mL). Stir overnight at roomtemperature under a nitrogen atmosphere. Add ethanol (10 mL) and stirfor an additional hour. Quench with acetic acid until the dark colorclears to a light yellow filter through celite and evaporate thefiltrate to an oil. Purify by silica gel chromatography to give thetitle compound.

Step d:d,l-cis-Pyrrolidine-4-methyl-2-tert-butylcarboxylate-3-ethylcarboxylate

Mix 4-dibenzylamino-3-methyl-2-tert-butyloxylyl-butyric acid, ethylester (10 g), 20% palladium hydroxide on carbon (1 g) and ethanol. Placeon a Paar Hydrogenation apparatus and hydrogenate at 30 psi for 3 hours.Filter and evaporate to an oil. Purify by silica gel chromatography togive the title compound.

Step e:d,l-cis-N-(9-Phenylfluorenyl)pyrrolidine-4-methyl-2-tert-butylcarboxylate-3-ethylcarboxylate

Mixd,l-cis-pyrrolidine-4-methyl-2-tert-butylcarboxylate-3-ethylcarboxylate(5 g), 9-phenylfluorenyl bromide (8.39 g, 26 mmol), lead nitrate (3.9 g,24 mmol), diisopropylethylamine (5 mL, 28 mmol) and acetonitrile (100mL). Stir at room temperature for 4 hours and add methylene chloride(200 ml). Fitler through silica gel and evaporate the filtrate to anoil. Purify by silica gel chromatography to give the title compound.

Step f:d,l-cis-N-(9-Phenylfluorenyl)-3-[(diethoxyphosphinyl)acetyl]pyrrolidine-4-methyl-2-carboxylicacid, tert-butyl ester

Dissolve diethyl methylphosphonate (9.25 g, 60 mmol) in anhydroustetrahydrofuran (50 mL), cool to -78° C. and place under a nitrogenatmsophere. Add n-butyllithium (37.5 mL of a 1.6M solution in hexane, 60mmol) and stir for 1/2 hour. Add a solution ofd,l-cis-N-(9-phenylfluorenyl)pyrrolidine-4-methyl-2-tert-butylcarboxylate-3-ethylcarboxylate(10.2 g, 20 mmol) in tetrahydrofuran (50 mL) and stir at -78° C. for 1hour. Quench with acetic acid and pour into saturated sodium chloride(100 mL). Extract with ethyl acetate (2×100 mL) and dry. Purify bysilica gel chromatography to give the title compound.

Step g: d,l-cis-3-(Phosphonoacetyl)pyrrolidine-4-methyl-2-carboxylicacid and d,l-trans-3-(Phosphonoacetyl]pyrrolidine-4-methyl-2-carboxylicacid

Stird,l-cis-N-(9-phenylfluorenyl)-3-[(diethoxyphosphinyl)acetyl]pyrrolidine-4-methyl-2-carboxylicacid, tert-butyl ester (3 g) with trifluoroacetic acid (30 mL) and water(1 mL). Blow to a residue with a stream of nitrogen, take up the residuein water (120 mL) and wash with ethyl acetate (75 mL). Freeze dry theaqueous phase to give a yellow oil. Dissolve the yellow oil inacetonitrile (20 mL) and methylene chloride (20 mL). Add trimethylsilyliodide (3.5 mL, 24 mmol) and stir for 5 hours. Pour into water (250 mL)and wash with toluene (3×250 mL). Freeze dry the aqueous phase to give asolid residue. Take up the solid residue in methanol (10 mL) andisopropanol (5 mL). Add propylene oxide (2 mL) and stir for 1 hour.Filter and dry to give the title compounds. Separate by High PerformanceLiguid Chromatography on a P/10 SAX M/20-24 (WHatman) Column with 0.025Mhydrochloric acid/acetonitrile to give the separate title compounds.

Example 16

d,l-cis-3-(Phosphonoacetyl)pyrrolidine-2-carboxylic acid andd,l-trans-3-(Phosphonoacetyl)pyrrolidine-2-carboxylic acid ##STR33##Step a: Ethyl 4-iodobutyrate

Mix ethyl 4-chlorobutyrate (80 g), acetone (400 mL) and sodium iodide(100 g). Reflux for 8 hours, cool and add methylene chloride (400 mL).Filter and evaporate the filtrate to a residue. Partition the residuebetween methylene chloride (200 mL) and water (200 mL). Separate theorganic phase, dry (MgSO₄) and evaporate to an oil. Purify bydistillation to give the title compound (89 g); bp 64° C. @ 0.5 mm Hg.

Step b: 4-Dibenzylaminobutyric acid, ethyl ester

Mix ethyl 4-iodobutyrate (43.5 g, 0.18 mol), dibenzylamine (35.5 g, 0.18mol), potassium carbonate (24.9 g, 0.18 mol) and ethanol (114 mL driedover 4A molecular sieves). Reflux for 24 hours then stir at roomtemperature for 48 hours. Add methylene chloride (100 mL) and filter.Evaporate the filtrate to a residue and purify by silica gelchromatography (methylene chloride) to give the title compound (47 g).

¹ H NMR (90 MHz, CDCl₃) ppm 3.95 (q, 2), 4.35 (s, 4 ), 2.40 (t, 2), 2.25(t, 2), 1.75 (q, 2), 1.1 (t, 3).

Step c: 4-Dibenzylamino-2-tert-butyloxylyl-butyric acid, ethyl ester

Mix 4-dibenzylaminobutyric acid, ethyl ester (19.5 g, 63 mmol),tert-butyl methyl oxylate (10 g, 63 mmol), potassium carbonate (9.3 g),ethanol (5 mL) and benzene (150 mL). Stir overnight at room temperatureunder a nitrogen atmosphere. Add ethanol (10 mL) and stir for anadditional hour. Quench with acetic acid until the dark color clears toa light yellow, filter through celite and evaporate the filtrate to anoil. Purify by silica gel chromatography (ethyl acetate/hexane) to givethe title compound.

Step d: d,l-cis-Pyrrolidine-2-tert-butylcarboxylate-3-ethylcarboxylate

Mix 4-dibenzylamino-2-tert-butyloxylyl-butyric acid, ethyl ester (10 g),20% palladium hydroxide on carbon (1 g) and ethanol. Place on a PaarHydrogenation apparatus and hydrogenate at 30 psi for 3 hours. Filterand evaporate to an oil. Purify by silica gel chromatography (90:10ethyl acetate/hexane) to give the title compound (5.2 g).

Step e:d,l-cis-N-(9-Phenylfluorenyl)pyrrolidine-2-tert-butylcarboxylate-3-ethylcarboxylate

Mix d,l-cis-pyrrolidine-2-tert-butylcarboxylate-3-ethylcarboxylate (5g), 9-phenylfluorenyl bromide (8.39 g, 26 mmol), lead nitrate (3.9 g, 24mmol), diisopropylethylamine (5 mL, 28 mmol) and acetonitrile (100 mL).Stir at room temperature for 4 hours and add methylene chloride (200ml). Fitler through silica gel and evaporate the filtrate to an oil.Purify by silica gel chromatography (70% ethyl acetate/hexane) to givethe title compound (9.5 g).

Step f:d,l-cis-N-(9-Phenylfluorenyl)-3-[(diethoxyphosphinyl)acetyl]pyrrolidine-2-carboxylicacid, tert-butyl ester

Dissolve diethyl methylphosphonate (9.25 g, 60 mmol) in anhydroustetrahydrofuran (50 mL), cool to -78° C. and place under a nitrogenatmsophere. Add n-butyllithium (37.5 mL of a 1.6M solution in hexane, 60mmol) and stir for 1/2 hour. Add a solution ofd,l-cis-N-(9-phenylfluorenyl)pyrrolidine-2-tert-butylcarboxylate-3-ethylcarboxylate(9.5 g, 20 mmol) in tetrahydrofuran (50 mL) and stir at -78° C. for 1hour. Quench with acetic acid and pour into saturated sodium chloride(100 mL). Extract with ethyl acetate (2×100 mL) and dry. Purify bysilica gel chromatography (70:30 ethyl acetate/hexane) to give the titlecompound (3.2 g).

¹ H NMR (300 MHz, CDCl₃) ppm 7.2-7.75 (m, 13), 4.05 (m, 4), 3.64 (d, 1),3.32 (t, 1), 3.15 (m, 2), 2.92 (dd, 1), 2.79 (m, 1), 2.35 (m, l), 1.8(m, 1), 1.29 (s, 9), 1.22 (m, 6).

Step g: d,l-cis-3-(Phosphonoacetyl)pyrrolidine-2-carboxylic acid andd,l-trans-3-(Phosphonoacetyl)pyrrolidine-2-carboxylic acid

Stird,l-cis-N-(9-phenylfluorenyl)-3-[(diethoxyphosphinyl)acetyl]pyrrolidine-2-carboxylicacid, tert-butyl ester (3 g) with trifluoroacetic acid (30 mL) and water(1 mL). Blow to a residue with a stream of nitrogen, take up the residuein water (120 mL) and wash with ethyl acetate (75 mL). Freeze dry theaqueous phase to give a yellow oil. Dissolve the yellow oil inacetonitrile (20 mL) and methylene chloride (20 mL). Add trimethylsilyliodide (3.5 mL, 24 mmol) and stir for 5 hours. Pour into water (250 mL)and wash with toluene (3×250 mL). Freeze dry the aqueous phase to give asolid residue. Take up the solid residue in methanol (10 mL) andisopropanol (5 mL). Add propylene oxide (2 mL) and stir for 1 hour.Filter and dry to give the title compounds (1.0 g). Separate by HighPerformance Liguid Chromatography on a P/10 SAX M/20-24 (Whatman) Columnwith 0.025M hydrochloric acid/acetonitrile to give the separate titlecompounds with the trans eluting first.

trans ¹ H NMR (300 MHz, D₂ O) ppm 4.8 (d, 1), 3.95 (m, 1), 3.55 (m, 1),3.2-3.5 (m, 3), 2.51 (m, 1), 2.28 (m, 1).

cis ¹ H NMR (300 MHz, D₂ O) ppm 4.59 (d, l), 4.19 (m, 1), 3.51 (m, 1),3.2-3.5 (m, 3), 2.49 (m, 1), 2.41 (m, 1).

The pyrrolidine compounds of Formula I wherein R₅ is linear C₁ -C₄ alkylor alkylphenyl can be prepared by techniques and procedures well knownand appreciated by one of ordinary skill in the art. A general syntheticprocedure for preparing these compounds is set forth in Scheme L. InScheme L all substituents unless otherwise indicated are as previouslydefined. ##STR34##

Scheme L provides a general synthetic procedure for preparing thepyrrolidine compounds of Formula I wherein R₅ is linear C₁ -C₄ alkyl oralkylphenyl.

In step a, the appropriated,l-cis-N-(9-phenylfluorenyl)pyrrolidine-2-alkylcarboxylate-3-ethylcarboxylateof structure (57) is alkylated with an appropriate alkylating agent ofthe formula R₅ '-Hal to give the correspondingd,l-cis-N-(9-phenylfluorenyl)pyrrolidine-2-alkylcarboxylate-3-alkyl-3-ethylcarboxylateof structure (60).

For example, the appropriated,l-cis-N-(9-phenylfluorenyl)pyrrolidine-2-alkylcarboxylate-3-ethylcarboxylateof structure (57) is contacted with a molar equivalent of a suitablenon-nucleophilic base, such as lithium diisopropylamide. The reactantsare typically contacted in a suitable organic solvent such astetrahydrofuran. The reactants are typically stirred together for aperiod of time ranging from 2-24 hours and at a temperature range offrom -78° C. to 0° C. Thed,l-cis-N-(9-phenylfluorenyl)pyrrolidine-2-alkylcarboxylate-3-alkyl-3-ethylcarboxylateof structure (60) is recovered from the reaction zone by alow-temperature quench into the appropriate alkylating agent of theformula R₅ '-Hal, followed by extraction by methods known in the art. Itmay be purified by silica gel chromatography.

In step b, the appropriated,l-cis-N-(9-phenylfluorenyl)pyrrolidine-2-alkylcarboxylate-3-alkyl-3-ethylcarboxylateof structure (60) is coupled with the appropriate phosphonate ester ofstructure (5) to give the correspondingd,l-cis-N-(9-phenylfluorenyl)-3-[(dialkoxyphosphinyl)acetyl]pyrrolidine-3-alkyl-2-carboxylicacid, ester of structure (61) as described previously in Scheme A, stepd.

In step c, the appropriated,l-cis-N-(9-phenylfluorenyl)-3-[(dialkoxyphosphinyl)acetyl]pyrrolidine-3-alkyl-2-carboxylicacid, ester of structure (61) is deprotected to give the correspondingd,l-cis-3-[(dialkoxyphosphinyl)acetyl]pyrrolidine-3-alkyl-2-carboxylicacid, ester of structure (62a) andd,l-trans-3-[(dialkoxyphosphinyl)acetyl]pyrrolidine-3-alkyl-2-carboxylicacid, ester of structure (62b) as described previously in Scheme A, stepf.

The appropriated,l-cis-3-[(dialkoxyphosphinyl)acetyl]pyrrolidine-3-alkyl-2-carboxylicacid, ester of structure (62a) andd,l-trans-3-[(dialkoxyphosphinyl)acetyl]pyrrolidine-3-alkyl-2-carboxylicacid, ester of structure (62b) can be separated into theirdiastereomeric pairs as shown previously in Scheme B.

In addition, the enantiomericaly pure3(S)-[(dialkoxyphosphinyl)acetyl]pyrrolidine-3-alkyl-2(R)-carboxylicacid, ester and enantiomericaly pure3(R)-[(dialkoxyphosphinyl)acetyl]pyrrolidine-3-alkyl-2(S)-carboxylicacid, ester can be prepared as set forth in Scheme K by subjecting theappropriated,l-cis-3-[(dialkoxyphosphinyl)acetyl]pyrrolidine-3-alkyl-2-carboxylicacid, ester of structure (62a) to an enzymatic hydrolysis as describedpreviously in Scheme D, step c and Scheme E, optional step d.

Similarly, the enantiomericaly pure3(S)-[(dialkoxyphosphinyl)acetyl]pyrrolidine-3-alkyl-2(S)-carboxylicacid, ester and enantiomericaly pure3(R)-[(dialkoxyphosphinyl)acetyl]pyrrolidine-3-alkyl-2(R)-carboxylicacid, ester can be prepared as set forth in Scheme K by subjecting theappropriated,l-trans-3-[(dialkoxyphosphinyl)acetyl]pyrrolidine-3-alkyl-2-carboxylicacid, ester of structure (62b) to an enzymatic hydrolysis as describedpreviously in Scheme D, step c and Scheme E, optional step d.

The appropriate 3-[(dialkoxyphosphinyl)acetyl]pyrrolidine-2-carboxylicacid, ester of Formula I described above in Scheme K can be furtherfunctionalized as described previously in Scheme A, steps g₁ -i.

The appropriated,l-cis-3-[(dialkoxyphosphinyl)acetyl]pyrrolidine-3-alkyl-2-carboxylicacid, ester of structure (62a) andd,l-trans-3-[(dialkoxyphosphinyl)acetyl]pyrrolidine-3-alkyl-2-carboxylicacid, ester of structure (62b) can be further functionalized asdescribed previously in Scheme A, steps g₁ -i.

The appropriate 3-[(functionalizedphosphinyl)acetyl]pyrrolidine-3-alkyl-2-carboxylic acid derivatives ofFormula I prepared as described above in Scheme L may also be furtherfunctionalized into the corresponding3-[1-imino-2-phosponoethyl]pyrrolidine-3-alkyl-2-carboxylic acidderivatives of Formula I as described previously in Scheme C, step a.

Starting materials for use in Scheme L are readily available to one ofordinary skill in the art.

The following examples present typical syntheses as described in SchemeL. These examples are intended to be illustrative only and are notintended to limit the scope of the present invention in any way.

Example 17

d,l-cis-3-(Phosphonoacetyl)pyrrolidine-3-methyl-2-carboxylic acid andd,l-trans-3-(Phosphonoacetyl]pyrrolidine-3-methyl-2-carboxylic acid##STR35## Step a:d,l-cis-N-(9-Phenylfluorenyl)pyrrolidine-2-tert-butylcarboxylate-3-methyl-3-ethylcarboxylate

Dissolve diisopropylamine (0.6 mL, 4.3 mmol) in tetrahydrofuran (10 mL)and cool to 0° C. Add, by dropwise addition, n-butyllithium (2.7 mL of a1.6M solution, 4.3 mmol). Stir for 1/2 hour, cool to -78° C. and add, bydropwise addition, a solution ofd,l-cis-N-(9-phenylfluorenyl)pyrrolidine-2-tert-butylcarboxylate-3-ethylcarboxylate(795mg, 1.6 mmol) in tetrahydrofuran (10 mL). Stir for 1 hour at -78° C.and then for 3 hours at -30° C. Transfer rapidly, via water heatedcannula, to a -78° C. solution of iodomethane (426 mg, 3 mmol) intetrahydrofuran (10 mL). Allow to warm to room temperature overnight.Add ethyl acetate and wash with brine. Evaporate to a residue and purifyby silica gel chromatography to give the title compound.

Step b:d,l-cis-N-(9-Phenylfluorenyl)-3-[(diethoxyphosphinyl)acetyl]pyrrolidine-3-methyl-2-carboxylicacid, tert-butyl ester

Dissolve diethyl methylphosphonate (9.25 g, 60 mmol) in anhydroustetrahydrofuran (50 mL), cool to -78° C. and place under a nitrogenatmsophere. Add n-butyllithium (37.5 mL of a 1.6M solution in hexane, 60mmol) and stir for 1/2 hour. Add a solution ofd,l-cis-N-(9-phenylfluorenyl)pyrrolidine-3-methyl-2-tert-butylcarboxylate-3-ethylcarboxylate(10.2 g, 20 mmol) in tetrahydrofuran (50 mL) and stir at -78° C. for 1hour. Quench with acetic acid and pour into saturated sodium chloride(100 mL). Extract with ethyl acetate (2×100 mL) and dry. Purify bysilica gel chromatography (70:30 ethyl acetate/hexane) to give the titlecompound.

Step c: d,l-cis-3-(Phosphonoacetyl)pyrrolidine-3-methyl-2-carboxylicacid and d,l-trans-3-(Phosphonoacetyl]pyrrolidine-2-carboxylic acid

Stird,l-cis-N-(9-phenylfluorenyl)-3-[(diethoxyphosphinyl)acetyl]pyrrolidine-3-methyl-2-carboxylicacid, tert-butyl ester (3 g) with trifluoroacetic acid (30 mL) and water(1 mL). Blow to a residue with a stream of nitrogen, take up the residuein water (120 mL) and wash with ethyl acetate (75 mL). Freeze dry theaqueous phase to give a yellow oil. Dissolve the yellow oil inacetonitrile (20 mL) and methylene chloride (20 mL). Add trimethylsilyliodide (3.5 mL, 24 mmol) and stir for 5 hours. Pour into water (250 mL)and wash with toluene (3×250 mL). Freeze dry the aqueous phase to give asolid residue. Take up the solid residue in methanol (10 mL) andisopropanol (5 mL). Add propylene oxide (2 mL) and stir for 1 hour.Filter and dry to give the title compounds (1.0 g). Separate by HighPerformance Liguid Chromatography on a P/10 SAX M/20-24 (Whatman) Columnwith 0.025M hydrochloric acid/acetonitrile to give the separate titlecompounds.

The compounds of Formula I are excitatory amino acid antagonists. Theyantagonize the effects which excitatory amino acids have upon the NMDAreceptor complex. They preferentially bind to the glutamate binding sitelocated on the NMDA receptor complex. They are useful in the treatmentof a number of disease states.

The compounds exhibit anti-convulsant properties and are useful in thetreatment of epilepsy. They are useful in the treatment of grand malseizures, petit mal seizures, psychomotor seizures, and autonomicseizures. One method of demonstrating their anti-epileptic properties isby the compounds ability to inhibit audiogenic convulsions in DBA/2mice. This test can be conducted in the following manner.

Typically one group of from 6-8 male DBA/2J audiogenic susceptible miceare administered from about 0.01 μg to about 100 μg of the testcompound. The test compound is administered intracerebrally into thelateral ventricle of the brain. A second group of mice are administeredan equal volume of a saline control by the same route. Five minuteslater the mice are placed individually in glass jars and are exposed toa sound stimulus of 110 decibels for 30 seconds. Each mouse is observedduring the sound exposure for signs of seizure activity. The controlgroup will have a statistically higher incidence of seizures than thegroup which receives the test compound.

Another method for demonstrating the anti-epileptic properties of thesecompounds is by their ability to inhibit the seizures that are caused bythe administration of quinolinic acid. This test can be conducted in thefollowing manner.

One group containing ten mice are administered 0.01-100 μg of testcompound intracerebroventricularly in a volume of 5 microliter ofsaline. A second control group containing an equal number of mice areadministered an equal volume of saline as a control. Approximately 5minutes later, both groups are administered 7.7 micrograms of quinolinicacid intracerebroventricularly in a volume of 5 microliters of saline.The animals are observed for 15 minutes thereafter for signs of clonicseizures. The control group will have a statistically higher rate ofclonic seizures than will the test group.

The compounds of Formula I are useful for preventing or minimizing thedamage which nervous tissues contained within the CNS suffer uponexposure to either ischemic, hypoxic, or hypoglycemic conditions.Representative examples of such ischemic, hypoxic, or hypoglycemicconditions include strokes or cerebrovascular accidents, carbon monoxidepoisoning, hyperinsulinemia, cardiac arrest, drownings, physical trauma,suffocation, and neonatal anoxic trauma. The compounds should beadministered to the patient within 24 hours of the onset of the hypoxic,ischemic, or hypoglycemic condition in order for the compounds toeffectively minimize the CNS damage which the patient will experience.

The compounds are also useful in the treatment of neurodegenerativediseases such as Huntington's disease, Alzheimer's disease, seniledementia, glutaric acidaemia type I, multi-infarct dementia, Parkinson'sdisease and neuronal damage associated with uncontrolled seizures. Theadministration of these compounds to a patient experiencing such acondition will serve to either prevent the patient from experiencingfurther neurodegeneration or it will decrease the rate at which theneurodegeneration occurs.

As is apparent to those skilled in the art, the compounds will notcorrect any CNS damage that has already occurred as the result of eitherdisease or a lack of oxygen or sugar. As used in this application, theterm "treat" refers to the ability of the compounds to prevent furtherdamage or delay the rate at which any further damage occurs.

The compounds exhibit an anxiolytic effect and are thus useful in thetreatment of anxiety. These anxiolytic properties can be demonstrated bytheir ability to block distress vocalizations in rat pups. This test isbased upon the phenomenon that when a rat pup is removed from itslitter, it will emit an ultrasonic vocalization. it was discovered thatanxiolytic agents block these vocalizations. The testing methods havebeen described by Gardner, C. R., Distress vocalization in rat pups: asimple screening method for anxiolytic drugs. J. Pharmacol. Methods. 14:181-187 (1985) and Insel et al., Rat pup ultrasonic isolation calls:Possible mediation by the benzodiapine receptor complex, Pharmacol.Biochem. Behav. 24: 1263-1267 (1986). The compounds also exhibit ananalgesic effect and are useful in controlling pain. The compounds mayalso be utilized to prophylacticaly prevent migraines or to terminate amigraine episode.

In order to exhibit any of these therapeutic properties, the compoundsneed to be administered in a quantity sufficient to inhibit the effectwhich the excitatory amino acids have upon the NMDA receptor complex.The dosage range at which these compounds exhibit this antagonisticeffect can vary widely depending upon the particular disease beingtreated, the severity of the patient's disease, the patient, theparticular compound being administered, the route of administration, andthe presence of other underlying disease states within the patient, etc.Typically the compounds exhibit their therapeutic effect at a dosagerange of from about 0.01 mg/kg/day to about 500 mg/kg/day for any of thediseases or conditions listed above. Repetitive daily administration maybe desirable and will vary according to the conditions outlined above.

The compounds of the present invention may be administered by a varietyof routes. They are effective if administered orally. The compounds mayalso be administered parenterally (i.e. subcutaneously, intravenously,intramuscularly, intraperitoneally, or intrathecally).

Pharmaceutical compositions can be manufactured utilizing techniquesknown in the art. Typically an antagonistic amount of the compound willbe admixed with a pharmaceutically acceptable carrier.

For oral administration, the compounds can be formulated into solid orliquid preparations such as capsules, pills, tablets, lozenges, melts,powders, suspensions, or emulsions. Solid unit dosage forms can becapsules of the ordinary gelatin type containing, for example,surfactants, lubricants and inert fillers such as lactose, sucrose, andcornstarch or they can be sustained release preparations. In anotherembodiment, the compounds of Formula I can be tableted with conventionaltablet bases such as lactose, sucrose, and cornstarch in combinationwith binders, such as acacia, cornstarch, or gelatin, disintegratingagents such as potato starch or alginic acid, and a lubricant such asstearic acid or magnesium stearate. Liquid preparations are prepared bydissolving the active ingredient in an aqueous or non-aqueouspharmaceutically acceptable solvent which may also contain suspendingagents, sweetening agents, flavoring agents, and preservative agents asare known in the art.

For parenteral administration the compounds may be dissolved in aphysiologically acceptable pharmaceutical carrier and administered aseither a solution or a suspension. Illustrative of suitablepharmaceutical carriers are water, saline, dextrose solutions, fructosesolutions, ethanol, or oils of animal, vegetative, or synthetic origin.The pharmaceutical carrier may also contain preservatives, buffers,etc., as are known in the art. When the compounds are being administeredintrathecally, they may also be dissolved in cerebrospinal fluid as isknown in the art.

As used in this application:

a) the term patient refers to warm blooded animals such as, for example,guinea pigs, mice, rats, cats, rabbits, dogs, monkeys, chimpanzees, andhumans;

b) the term treat refers to the ability of the compounds to eitherrelieve, alleviate, prevent or slow the progression of the patient'sdisease;

c) the term neurodegeneration refers to a progressive death anddisappearance of a population of nerve cells occurring in a mannercharacteristic of a particular disease state and leading to braindamage.

The compounds may also be admixed with any inert carrier and utilized inlaboratory assays in order to determine the concentration of thecompounds within the serum, urine, etc., of the patient as is known inthe art.

Neurodegenerative diseases are typically associated with a loss of NMDAreceptors. Thus, the compounds of Formula I may be utilized indiagnostic procedures to aid physicians with the diagnosis ofneurodegenerative diseases. The compounds may be labeled with isotopicagents by techniques known in the art and utilized as imaging agents.They may then be administered to a patient in order to determine whetherthe patient is exhibiting a decreased number of NMDA receptors and therate at which that loss is occurring.

What is claimed is:
 1. A compound of the formula: ##STR36## in which R₁is represented by hydrogen, C₁₋₄ alkyl or CF₃ ; M is represented by O,N--O--R₄ or ##STR37## in which R₄ is represented by hydrogen, C₁₋₄ alkylor phenyl (C₁₋₃ alkyl);A is represented by: ##STR38## in which R₂ isrepresented by hydrogen, C₁₋₄ alkyl, cyclopentyl, cyclohexyl, ##STR39##phenyl, substituted phenyl in which the phenyl moiety is substitutedwith up to 3 substituents with each substituent being independentlyselected from the group consisting of halogens, C₁ -C₄ alkyl, C₁ -C₄alkoxyl, CF₃, OCF₃, OH, CN, COOR₆ and CONR₆ R₇, phenyl (C₁₋₃ alkyl) inwhich the phenyl moiety may be optionally substituted; R₅ is representedby hydrogen, linear C₁₋₄ alkyl, or phenyl (C₁₋₃ alkyl); R' isrepresented by hydrogen, C₁₋₄ alkyl, phenyl, phenyl (C₁₋₃ alkyl), orcyclohexylmethyl; R₆ and R₇ are each represented by hydrogen or a C₁ -C₄alkyl;in which n is represented by an integer from 2-4 and Alk and Alk₁are each represented by a C₁₋₄ alkyl; or a pharmaceutically acceptablesalt thereof.
 2. A compound according to claim 1 wherein M is O.
 3. Acompound according to claim 1 wherein M is N--O--R₄.
 4. A compoundaccording to claim 1 wherein M is ##STR40##
 5. A method for antagonizingthe effects of excitatory amino acids upon the NMDA receptor complexcomprising administering to a patient in need thereof, an antagonisticamount of a compound according to claim
 1. 6. A method for the treatmentof epilepsy comprising administering to a patient in need thereof ananti-epileptic amount of a compound according to claim
 1. 7. A methodfor the treatment of neurodegenerative diseases comprising administeringto a patient in need thereof an effective amount of a compound accordingto claim
 1. 8. A method for preventing ischemic/hypoxic/hypoglycemicdamage to cerebral tissue comprising administering to a patient in needthereof an effective amount of a compound according to claim
 1. 9. Amethod for the treatment of anxiety comprising administering ananxiolytic amount of a compound according to claim
 1. 10. A method forproducing an analgesic effect comprising administering to a patient inneed thereof an analgesic amount of a compound according to claim
 1. 11.A pharmaceutical composition comprising a compound according to claim 1in admixture with a pharmaceutically acceptable carrier.
 12. A compoundaccording to claim 1 in which said compound isd,l-cis-3-(phosphonoacetyl)pyrrolidine-4-methyl-2-carboxylic acid.
 13. Acompound according to claim 1 in which said compound isd,l-trans-3-(phosphonoacetyl)pyrrolidine-4-methyl-2-carboxylic acid. 14.A compound according to claim 1 in which said compound isd,l-cis-3-(phosphonoacetyl)pyrrolidine-2-carboxylic acid.
 15. A compoundaccording to claim 1 in which said compound isd,l-trans-3-(phosphonoacetyl)pyrrolidine-2-carboxylic acid.
 16. Acompound according to claim 1 in which said compound isd,l-cis-3-(phosphonoacetyl)pyrrolidine-3-methyl-2-carboxylic acid.
 17. Acompound according to claim 1 in which said compound isd,l-trans-3-(phosphonoacetyl)pyrrolidine-3-methyl-2-carboxylic acid.